feat(ui): show project title in pane headers

[j35dev]

Split pane headers currently show only the session title. When two panes from different projects are open, that is not enough to tell them apart.

What changed

• Pane chrome now labels a session as Project title - Session title (e.g. Ari - New session).
• Unfiled / ad-hoc sessions keep the session title alone.
• Truncated headers expose the full label on hover.
• Close buttons and pane menus use the same combined name.

Why

A split layout with more than one project needs the project name in the pane head so the session is identifiable at a glance.

How verified

VITEST_MAX_WORKERS=2 pnpm verify green (typecheck + lint + tests).
Desktop: 155 passed, 3 skipped (1411 tests).

[devin-ai-integration]

Devin Review found 1 potential issue.

[devin-ai-integration]

🟡 Closed projects remain in pane titles

When a project is closed, titleOf still prefixes its sessions with that project's name. Closed projects remain in projects, although their sessions are Unfiled.

Learn more

A closed project stays in the project registry with open: false. Its sessions are grouped under Unfiled by sidebarGroups, but this lookup matches every registry entry. The pane therefore retains a project prefix after the user closes that project.

Example: Closing the “Docs” project moves “Draft notes” beneath Unfiled. Its pane still reads “Docs - Draft notes” instead of “Draft notes”.

Recommended fix: Restrict the name lookup to open projects, matching the sidebar's filing rule.

Suggested change

	const projectName =
	session.projectId === UNFILED_GROUP_ID
	? null
	: (projects.find((p) => p.id === session.projectId)?.name ?? null)
	const projectName =
	session.projectId === UNFILED_GROUP_ID
	? null
	: (projects.find((p) => p.open && p.id === session.projectId)?.name ??
	null)

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