fix: reapply sidebar project selection

[wibus-wee]

Summary

• make every desktop sidebar project-row activation reapply that project to the mounted Composer
• deliver repeated same-project activations through a transient in-process request instead of URL or history state
• keep the existing stable route search only for navigation, refresh, and deep-link restoration
• leave mobile behavior unchanged and avoid adding a secondary hover-only action

Testing

• vitest run packages/components/tests/chat-landing-project-selection.test.ts packages/components/tests/chat-landing-derived.test.ts (59 tests passed)

Full package typecheck was not run from this worktree because its dependencies are not installed; CI should perform the authoritative check.