fix(app): refresh v2 tab titles

[gzb1128]

Issue for this PR

Fixes #30329

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Fixes the v2 layout tab bar not refreshing when the model generates a session title.

Root cause: mapArray runs its mapper inside untrack, so reading session.title inside the mapper creates no reactive subscription. When the store is later updated via reconcile (in the session.updated SSE handler), the mapped result stays stale.

Fix: Extract tab enrichment into createTitlebarTabsEnriched() (titlebar-tabs.ts). Instead of eagerly reading session data inside the untracked mapper, the helper stores the session accessor and exposes title as a reactive getter:

const base = mapArray(() => tabsStore, (tab) => {
  const info = sessionForTab(tab)  // accessor, not value
  return { ...tab, info, title: () => info()?.title }
})
return () => base().filter((tab) => tab.info())

The <For> render function now calls tab.title() and tab.info() under a tracking scope, so updates propagate correctly.

How did you verify your code works?

• Reproduced the regression: old mapper captures session.title as a static snapshot, test asserts stale value
• bun test --preload ./happydom.ts ./src/components/titlebar.test.ts from packages/app: 1 pass
• bun typecheck from packages/app: no new errors (pre-existing message-timeline.tsx error unrelated)
• git diff --check: clean

Checklist

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

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