🎨 Palette: Add tooltips to icon-only buttons

[NotEduCo342]

💡 What: Added tooltip properties to multiple IconButton widgets across the app (search clearing, sending messages, editing avatars).
🎯 Why: Icon-only buttons without labels can be confusing for users unfamiliar with the specific icons, especially on desktop/web where hover states are expected.
♿ Accessibility: In Flutter, the tooltip property also acts as the semantic label for screen readers. By adding these, we significantly improve the app's keyboard and screen reader accessibility.

---

PR created automatically by Jules for task 8489942958510127359 started by @NotEduCo342

[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.