style(tui): UI polish pass (v0.5.1)

Cosmetic refinements on top of v0.5.0's content-only main pane. No
behavior change; ships as a patch bump.

## Color signal — terminal labels tinted per outcome

The transcript's [done]/[error]/[cancelled] labels were plain
foreground (Australis #a9bcc3 white), which made them slow to scan
against the surrounding assistant text. Now tinted per outcome:

- [done]      → Aurora green   (#16B866 / $success)
- [error]     → Dawn red       (#ff491a / $error)
- [cancelled] → Dawn yellow    (#e1c631 / $warning)

The post-Done Rule() separator is also tinted to Australis dark-60
(#86929d) so the streamed-text → markdown-body boundary reads as
chrome, not a content artifact.

## Empty-state placeholders

Tools and Debug panes were stark-empty before any turn fired — easy
to misread as "the pane is broken." Now show placeholder lines on
mount in Sea dark-50 italic:

  Tools tab: (no tool events yet — start a turn that uses tools)
  Debug tab: (waiting for telemetry — start a turn)

The placeholders scroll off naturally as real events fill the panes.

## Live thinking widget self-explains

The thinking-current Static at the top of the right column used to
just display raw thinking content with no context — an operator
glancing at the screen mid-stream might not realize they were
looking at LLM chain-of-thought. Now prefixed with "thinking… " so
the widget self-identifies.

## Spacing + chrome

- Transcript / tools-log / debug-log: 1-cell horizontal padding so
  content doesn't hug the column border.
- thinking-current: italic text-style on top of the dark-60 color,
  so the live-preview band is visually distinct from solid-colored
  log content.
- Active tab in TabbedContent: Aurora bright-cyan label + bold
  text-style, so the eye lands on the currently selected pane.
- Input placeholder text: tinted to Sea dark-50 so it reads as
  placeholder, not content.

## Test impact

3 new tests added (test_done_label_styled_success,
test_empty_state_placeholders_present, plus the polish hits
test_thinking_widget_truncation / test_thinking_coalesce updated for
the "thinking… " prefix). 4 existing tests that checked
`isinstance(w, str) and w.startswith("[done]")` updated to use the
_text_of helper (terminal labels are now RichText, not str).
_spy_writes helper widened to accept positional args after Textual's
internal deferred-render path started passing them positionally
post-Resize.

241/241 GREEN; ruff clean. Live smoke against personal Worldtree
confirmed: Done line renders in Aurora green #16B866 verbatim;
both placeholder lines appear in dark-50; thinking widget shows
"thinking… <content>" during a turn.

Patch bump (v0.5.0 → v0.5.1) per SemVer etiquette: purely cosmetic;
no signature change; no caller-visible behavioral shift.

tests/test_tui.py

@@ -61,13 +61,18 @@ def _args_existing(session_id: str = "s-1existing", **overrides) -> ParsedArgs:
 
 
 def _spy_writes(monkeypatch) -> list:
-    """Patch RichLog.write to record every arg into a list (returned)."""
+    """Patch RichLog.write to record every arg into a list (returned).
+
+    Accepts *args/**kwargs so Textual's internal deferred-render path
+    (which calls write positionally with width/expand/shrink/scroll_end)
+    still works after a write-during-mount + Resize sequence.
+    """
     writes: list = []
     original = RichLog.write
 
-    def spy(self, content, **kw):
+    def spy(self, content, *args, **kw):
         writes.append(content)
-        return original(self, content, **kw)
+        return original(self, content, *args, **kw)
 
     monkeypatch.setattr(RichLog, "write", spy)
     return writes
@@ -147,8 +152,9 @@ class TestTuiPresenterState:
         )
         # Widget updated 3 times — once per delta — with cumulative content
         assert widget.update.call_count == 3
-        # Latest call shows the full accumulated content (under 200 chars so no truncation)
-        assert widget.update.call_args_list[-1][0][0] == "abc"
+        # Latest call shows the full accumulated content (under 200 chars so no truncation).
+        # v0.5.1 polish: widget text is prefixed with "thinking… " for self-explanation.
+        assert widget.update.call_args_list[-1][0][0] == "thinking… abc"
         # Widget became visible at first delta
         assert widget.display is True
         # No RichLog write yet — closure hasn't fired
@@ -218,9 +224,11 @@ class TestTuiPresenterState:
             raw=False,
         )
         last_update = widget.update.call_args_list[-1][0][0]
-        # …-prefix + last-200 = 201 chars
-        assert last_update.startswith("…")
-        assert len(last_update) == 201
+        # v0.5.1 polish: widget gets a "thinking… " prefix + ellipsis-truncated tail.
+        assert last_update.startswith("thinking… ")
+        # tail is "…" + last-200 = 201 chars; prefix is 10 chars ("thinking… ")
+        assert len(last_update) == len("thinking… ") + 201
+        assert "…" in last_update
 
     def test_thinking_widget_visibility_lifecycle(self) -> None:
         """thinking_widget_visibility_lifecycle [trace]: hidden at start; visible during thinking;
@@ -426,8 +434,8 @@ class TestTuiPresenterState:
         writes = [c[0][0] for c in log.write.call_args_list]
         # Text stream wrote "hi" with no prefix.
         assert "hi" in writes
-        # [done] label wrote.
-        assert any(isinstance(w, str) and w.startswith("[done]") for w in writes)
+        # v0.5.1: [done] label is now RichText (Aurora green); plain content test via _text_of.
+        assert any(_text_of(w).startswith("[done]") for w in writes)
         # Rule + Markdown render present (post-Done body re-render per issue #4 INV-005).
         assert any(isinstance(w, Rule) for w in writes)
         assert any(isinstance(w, Markdown) for w in writes)
@@ -623,9 +631,9 @@ class TestTuiPresenterState:
             raw=True,
         )
         done_line = next(
-            c[0][0]
+            _text_of(c[0][0])
             for c in log.write.call_args_list
-            if isinstance(c[0][0], str) and c[0][0].startswith("[done]")
+            if _text_of(c[0][0]).startswith("[done]")
         )
         assert "duration=5.5s" in done_line
         assert "duration_ms=5467" not in done_line
@@ -651,9 +659,9 @@ class TestTuiPresenterState:
             raw=True,
         )
         done_line = next(
-            c[0][0]
+            _text_of(c[0][0])
             for c in log.write.call_args_list
-            if isinstance(c[0][0], str) and c[0][0].startswith("[done]")
+            if _text_of(c[0][0]).startswith("[done]")
         )
         assert "usage 6756 in → 126 out (6882 total, 0 cached)" in done_line
 
@@ -914,6 +922,59 @@ class TestLayoutShape:
             await pilot.pause()
             assert app.query_one("#side-panes", TabbedContent).active == "debug-tab"
 
+    async def test_done_label_styled_success(self) -> None:
+        """done_label_styled_success [v0.5.1]: [done] label renders in Aurora green."""
+        from rich.text import Text as RichText
+        from textual.widgets import RichLog
+
+        app = _resolved_app(_args_new(), session_id="s-new12345", agent_id="mimir")
+        async with app.run_test() as pilot:
+            await pilot.pause()
+            # Probe the presenter directly — write a Done via state.render.
+            from ratatoskr.tui import TuiPresenterState
+            log = app.query_one("#transcript", RichLog)
+            state = TuiPresenterState()
+            seen: list = []
+            orig = log.write
+            log.write = lambda c, *a, **kw: (seen.append(c), orig(c, *a, **kw))[1]
+            state.render(
+                _make_tui_done(),
+                log=log,
+                thinking_widget=app.query_one("#thinking-current"),
+                tools_log=app.query_one("#tools-log", RichLog),
+                debug_log=app.query_one("#debug-log", RichLog),
+                raw=True,
+            )
+            done = next(
+                c for c in seen
+                if isinstance(c, RichText) and _text_of(c).startswith("[done]")
+            )
+            assert done.style == "#16B866"  # Aurora green
+
+    async def test_empty_state_placeholders_present(self) -> None:
+        """empty_state_placeholders_present [v0.5.1]: tools-log + debug-log show
+        placeholder lines before any turn fires."""
+        from textual.widgets import RichLog
+
+        app = _resolved_app(_args_new(), session_id="s-new12345", agent_id="mimir")
+        async with app.run_test() as pilot:
+            await pilot.pause()
+            # Activate Debug tab so its content actually renders.
+            from textual.widgets import TabbedContent
+            tabbed = app.query_one("#side-panes", TabbedContent)
+            tabbed.active = "debug-tab"
+            await pilot.pause()
+            tabbed.active = "tools-tab"
+            await pilot.pause()
+            tools_log = app.query_one("#tools-log", RichLog)
+            debug_log = app.query_one("#debug-log", RichLog)
+            tools_text = " ".join(str(line) for line in tools_log.lines)
+            tabbed.active = "debug-tab"
+            await pilot.pause()
+            debug_text = " ".join(str(line) for line in debug_log.lines)
+            assert "no tool events" in tools_text
+            assert "waiting for telemetry" in debug_text
+
     async def test_pane_name_updates_on_tab_switch(self) -> None:
         """pane_name_updates_on_tab_switch [v0.5.0]: pane-name reflects active tab.