dock Claude's task list above the composer (T-308)

Claude's TodoWrite checklist was invisible. Add a TaskItem/TaskStatus
model + a latest-wins parser (taskListFrom) that reads the most recent
TodoWrite tool call (it replaces the whole list each time), and a compact
display-only ClaudeTaskDock pinned between the conversation and the
composer: collapsed to "N tasks · M done" + the current in-progress item,
expandable to the full checklist with per-item status glyphs + a11y
labels. Hidden when there are no tasks. Parser + widget tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -18,6 +18,11 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
+- **Claude's task list is now visible, docked above the composer.** When Claude
+  is tracking a TodoWrite checklist, a compact display-only strip shows it pinned
+  above the input — collapsed to `N tasks · M done` + the current in-progress
+  item, expandable to the full list with per-item status glyphs. Hidden when
+  there are no tasks. (T-308)
 - **A "Deny & simplify" option on the permission card.** Alongside Allow /
   Allow-and-remember / Deny, a fourth button denies the action with a
   preformatted note telling Claude it was too complex for the permission system