style(tui): kill remaining blue + thinking-current into pane (v0.6.1)

Three operator-flagged issues:

## 1. "Background is still blue" — Header sub-widgets + scrollbar

Two surviving blue sources after v0.6.0:

- **Header sub-widgets** (HeaderIcon, HeaderTitle, HeaderClock) each
  carry their own `$primary` tint that the parent
  `Header { background }` rule alone doesn't override. Sub-selectors
  added: `Header, HeaderIcon, HeaderTitle, HeaderClock { background:
  $surface; color: $au-bright-blue; }`.
- **Scrollbar gutter** uses Textual's `$primary-tint` (#32436a) by
  default. Per-widget scrollbar overrides: `ListView` (picker) and
  `RichLog` (every pane) get explicit Sea darks for gutter + thumb.

Live verification: both AgentPickerApp and RatatoskrApp now render
ZERO instances of `#6388d8` (Aurora blue) or `#32436a` (its dark
derivative) in the export-screenshot SVG.

## 2. "Picker is bright cyan with unreadable text" — ListView focus

Textual's default `ListView:focus > ListItem.--highlight { background:
$primary }` was overriding my v0.6.0 `#agent-list > ListItem.--highlight
{ background: $au-dark-30 }` because `:focus` carries higher
specificity. The highlighted item was rendering with Aurora-blue
background + bright-blue text = unreadable.

Fix: both selectors targeted explicitly with sufficient specificity:
`ListView > ListItem.--highlight, ListView:focus > ListItem.--highlight
{ background: $au-dark-30 }`. Description text bumped to Sea bright-70
for better contrast against the dark-30 highlight.

## 3. "Streaming everywhere, should just stream in line"

User flagged the disconnect: live thinking rendered above the
TabbedContent in the right-column header, then on closure the content
"moved" to thinking-log inside the Thinking pane. Read as jarring
discontinuity.

Fix: `thinking-current` Static moved INTO the Thinking TabPane (docked
bottom), below `thinking-log`. Both surfaces co-located now — live
streaming + closed runs share the same pane. Operator switches to
Ctrl+3 (Thinking) to see chronological closed runs ABOVE + live
streaming line BELOW. Same pattern as the transcript: closed history
+ inline streaming tail.

Trade-off: live thinking is now visible only when on the Thinking
tab. Pre-v0.6.1 it was always visible above the tabs. The user
explicitly prefers the co-located shape; this is the right call.

## Contract amendment

docs/contracts/issues/13.contract.md INV-024 amended: thinking-current
now docks bottom of the Thinking TabPane (was right-column header).
v0.6.0 layout-spec snapshot updated to reflect the new shape. Drift-
check clean.

## Tests + smoke

241/241 GREEN; ruff clean. Live smoke against personal Worldtree
confirmed:
- thinking-current AND thinking-log both inside thinking-tab.walk_children().
- Post-Done state: 23 closed-run lines in thinking-log, thinking-current
  cleared to empty.
- Picker exports zero blue rects; main App exports zero blue rects.

Patch bump (v0.6.0 → v0.6.1): purely cosmetic + layout adjustment
within the existing pane structure; no public-API change.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "ratatoskr"
-version = "0.6.0"
+version = "0.6.1"
 description = "Worldtree Conversation API debug TUI — multi-pane observability dashboard"
 readme = "README.md"
 requires-python = ">=3.12"