fix(app): todo dock reactivity to in-place todo updates

[lexlian]

Issue for this PR

Closes #33063

Type of change

• Bug fix

What does this PR do?

The SessionTodoDock rendered its todo list with Solid's <Index>, which only re-renders when the array length or item references change. The global todo store (serverSync().data.session_todo[id]) is updated via reconcile(todos, { key: "id" }), which preserves object references for matched IDs — so in-place status/content changes were invisible to <Index>.

When the todowrite tool flipped a todo's status from pending to completed or updated its content text, the dock's checkboxes stayed stale until a full page reload.

Switching <Index> to <For> diffs by value reference and re-runs the render prop when an item updates. <For> is the same primitive the TUI sidebar uses (packages/tui/src/feature-plugins/sidebar/todo.tsx:26), which works correctly today.

Single file change in packages/app/src/pages/session/composer/session-todo-dock.tsx:

• Import: add For to the solid-js import
• Inside TodoList: swap <Index> for <For> and update the render-prop signature from accessor (todo) => todo() to value (todo) => todo

The parent SessionTodoDock retains its <Index each={progress()}> for stable progress label tokens (unchanged).

How did you verify your code works?

• bun run typecheck on the app package — no new errors introduced (25 pre-existing errors in unrelated files on origin/dev confirmed unchanged)
• bun test on the app package — 406 pass / 1 fail, identical to origin/dev baseline (the 1 failure is a missing @pierre/trees module in pierre-tree.test.ts, unrelated)
• Traced root cause through Solid source: packages/app/node_modules/solid-js/dist/dev.js:1244-1286 (indexArray) shows <Index> only updates per-item signals when items[i] !== newItems[i], which is false for items preserved by reconcile({ key: "id" })
• Confirmed TUI is unaffected: uses <For each={list()}> with direct value access (item.status, item.content)
• Confirmed bug exists on origin/dev (009f3799c) via git show of all affected files

Screenshots / recordings

N/A — desktop-only render fix verifiable via DOM state, requires interactive session with todowrite tool calls.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR