refactor(tui): thinking streams into whole pane (v0.6.5)

Operator: "Why does the thinking scroll a little section at the
bottom of the thinking pane instead of scrolling the whole pane?"

Root cause: v0.6.1's thinking-current Static was docked to the
bottom of the Thinking pane and rendered the last 200 chars of
streaming content. As deltas arrived, the displayed 200-char tail
shifted — old text fell off the left, new text appeared on the
right — visually reading as "a little section scrolling at the
bottom" while the larger thinking-log RichLog above showed only
the previous run's closed content (or nothing on first turn).

## Fix: stream directly into thinking-log

The Static is gone. Thinking deltas now write straight to the
`thinking-log` RichLog (one delta = one line in the scrollable
log). The whole pane scrolls naturally as content arrives —
operator can switch to Ctrl+3 and see streaming content fill
the pane top-to-bottom.

Routing pattern:

  First Thinking delta of run:
    → write Rule(title="turn N · thinking #K start") to thinking_log
    → write delta content as a line
    → set thinking_open = True
  Subsequent Thinking deltas:
    → write delta content as a line
  Non-thinking event (closes the run):
    → write Rule(title="turn N · thinking #K end") to thinking_log
    → reset thinking_open

The Rule(start) at the top of an in-progress run is now the
"thinking is happening" indicator. No more separate live-preview
widget required.

## Trade-off: no markdown re-render

Pre-v0.6.5 closed runs got a Markdown(full_content) render between
the start/end Rules. v0.6.5 drops that — the streamed deltas ARE
the content; re-rendering as Markdown would either need to wait
for run-end (no streaming) OR re-render incrementally per delta
(bad UX). Streaming wins for "live observability" framing.

The downside: if model thinking has Markdown structure (lists,
code), it renders as raw text. Acceptable per operator's "stream
in line" framing.

## Removed widgets

- `Static#thinking-current` (right column / Thinking pane bottom)
- `TuiPresenterState.render` no longer takes a `thinking_widget` param
- `TuiPresenterState.thinking_buffer` field dropped (no accumulation)
- `_stream_turn_worker` no longer queries `#thinking-current`
- `on_mount` no longer hides `#thinking-current`
- DEFAULT_CSS `#thinking-current` block removed

## Contract amendment

INV-022 amended: thinking now streams as raw delta lines, not
Markdown-rendered on close. INV-024 amended: thinking-current
Static removed entirely (was relocated v0.6.1, removed v0.6.5).
Drift-check clean.

## Tests

238/238 GREEN (was 241 — 3 obsolete widget tests deleted:
test_thinking_widget_truncation, test_thinking_widget_visibility_lifecycle,
test_terminal_events_belt_and_braces_widget_cleanup). 5 routing tests
rewritten for the new streaming shape (test_thinking_streams_into_thinking_log,
test_thinking_closes_to_thinking_log, test_multiple_thinking_runs_...,
test_render_exception_fallback, test_cancelled_mid_thinking_closes,
test_left_column_content_only).

ruff clean. Manual injection test confirms routing: Rule(start) +
delta lines write to thinking_log; transcript untouched.

Patch bump (v0.6.4 → v0.6.5) — internal restructure within Thinking
pane; presenter signature narrowed; no caller-visible public API
change (RatatoskrApp + AgentPickerApp surfaces identical).

docs/contracts/issues/13.contract.md

@@ -161,9 +161,9 @@ New `Static(id="pane-name")` widget alongside the existing `identity` + `hint` w
 - **INV-019** *(amended v0.6.0)*: Three TabPanes in the right column: `Tools` (id `tools-tab`, contains `#tools-log`) + `Debug` (id `debug-tab`, contains `#debug-log`) + `Thinking` (id `thinking-tab`, contains `#thinking-log`). Ctrl+1/Ctrl+2/Ctrl+3 activate respective tabs. `pane-name` Static reflects active tab name dynamically.
 - **INV-020** *(amended v0.6.0)*: Render-exception fallback (INV-009) preserves routing per event class: `ToolStart` / `ToolResult` → `tools_log`; `Thinking` → `thinking_log`; `WorkerPhase` / `TextBoundary` → `debug_log`; everything else → `log`.
 - **INV-021** *(new v0.6.0)*: `Text` events do NOT route to `log` per-delta. They accumulate into `TuiPresenterState.text_buffer` and update a single `current_text` Static (docked above the prompt). On terminal event (`Done`/`Error`/`Cancelled`), `current_text` is cleared and (raw mode) accumulated text or (non-raw) post-Done `Markdown(response)` is written to `log`. The pre-v0.6.0 per-token RichLog spam is retired.
-- **INV-022** *(new v0.6.0)*: Closed thinking runs route to `thinking_log`, NOT `debug_log`. Each closed run writes three entries: `Rule(title=f"turn N · thinking #K start")`, `Markdown(content)`, `Rule(title=f"turn N · thinking #K end")` — the model's chain-of-thought is presented as rendered Markdown (model reasoning often has lists / code / structure) wrapped in operator-visible start/end markers. `thinking_run_index` increments per-run within a turn.
+- **INV-022** *(amended v0.6.5)*: Thinking deltas stream DIRECTLY into `thinking_log` (one delta = one RichLog line). The first delta of a run writes `Rule(title=f"turn N · thinking #K start")`; subsequent deltas write their raw content as lines; the run closes on the next non-thinking event with `Rule(title=f"turn N · thinking #K end")`. Pre-v0.6.5 markdown re-render dropped — the streamed deltas ARE the content; the whole pane scrolls naturally as content arrives.
 - **INV-023** *(new v0.6.0)*: Turn-ID header `Rule(title=f"turn N")` is written to all four log panes (`log`, `tools_log`, `debug_log`, `thinking_log`) by `_stream_turn_worker` on the first event of each turn — enables cross-pane visual correlation during multi-turn debugging.
-- **INV-024** *(amended v0.6.1)*: `thinking-current` Static lives INSIDE the Thinking TabPane (docked bottom, below `thinking-log`) — co-located with closed thinking runs so the operator sees streaming + history in one pane. Pre-v0.6.1 it sat above the TabbedContent (right-column header) which created a top/bottom discontinuity; the co-located shape resolves that. Trade-off: live thinking is now visible only when the Thinking tab is active (Ctrl+3). Prefix `thinking… ` self-identifies the widget contents.
+- **INV-024** *(amended v0.6.5)*: `thinking-current` Static REMOVED. v0.6.1 placed it inside the Thinking pane (docked bottom); operators reported the bottom-docked Static "scrolling a little section at the bottom" (its 200-char tail acting as a scroll-window) instead of letting the whole pane scroll. v0.6.5 deletes the Static entirely and streams Thinking deltas directly into `thinking_log` (the scrollable RichLog) — the whole pane scrolls naturally as content arrives. The Rule(start) at the first delta of a run is now the live "thinking is happening" indicator.
 
 ## TESTS (additions / changes to test_tui.py)