Feat: Add GeoJSON export functionality

[google-labs-jules]

This commit introduces a new feature that allows users to export all their notes as a GeoJSON file.

A new menu component has been added to the left of the note input field. This menu contains an "Export as GeoJSON" option, which, when clicked, generates a GeoJSON file containing all notes with their location, timestamp, and content.

The new component is styled to match the existing application aesthetic.

---

PR created automatically by Jules for task 288807777619096017

[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!

---

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

[benfoxall]

How about using the <dialog> element for the menu?

[google-labs-jules]

How about using the <dialog> element for the menu?

That's a great suggestion! I've refactored the component to use the <dialog> element for better accessibility and to leverage modern browser features. The functionality remains the same, but the implementation is now more robust. Thank you for the feedback!