🎨 Palette: Add interactive "Pro Tips" to search interface

[AhmmedSamier]

This PR adds a delightful "Pro Tip" feature to the DeepLens search interface.

What:

• A "Pro Tip" item is displayed at the bottom of the "Welcome" (empty state) and "Recent History" lists.
• The tip displays a random helpful hint about DeepLens features (e.g., using # for symbols or /m for modified files).
• The item is interactive: selecting it (clicking or pressing Enter) cycles to the next tip without closing the search window.

Why:

• Many users may not be aware of the powerful slash commands and shortcuts available in DeepLens.
• This feature provides a non-intrusive, "just-in-time" learning mechanism.
• It adds a touch of personality and polish ("Palette's Philosophy").

Accessibility:

• The item uses standard VS Code QuickPickItem structure.
• It has a clear label ($(light-bulb) Pro Tip: ...) and description.
• It is keyboard accessible (focusable and actionable).

Testing:

• Verified with static analysis (tsc, eslint).
• Verified build process (bun run compile).
• Note: Integration tests were skipped due to environment limitations (no display for VS Code UI tests), but the logic is isolated and safe.

---

PR created automatically by Jules for task 13715851749417294704 started by @AhmmedSamier

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.