fix(app): improve desktop project switching performance

[kunish]

Issue for this PR

Closes #16256

Type of change

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

What does this PR do?

This PR improves desktop project switching responsiveness by reducing synchronous work on the switch path.

Main changes:

• avoid full root-session sorting when only top/latest items are needed (topRootSessions, latestRootSession, nextRootStart)
• optimize navigateToProject with fast-path logic and fewer blocking updates
• make sidebar preview/workspace session calculations lazy and visibility-driven
• reduce immediate session-page render cost by gating heavy timeline rendering behind existing defer behavior
• improve project metadata enrichment so VCS-derived workspace controls behave correctly

How did you verify your code works?

• bun typecheck (packages/app)
• PLAYWRIGHT_PORT=4444 bun test:e2e -- e2e/projects/projects-switch.spec.ts
• bun test:e2e:local -- e2e/projects/projects-switch.spec.ts

Screenshots / recordings

No UI visuals attached for this round.

Checklist

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

[github-actions]

Hey! Your PR title perf(app): improve desktop project switch performance doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍