For the extension devs:

Adds a `RebuildDevExtension` action that triggers a rebuild of an
installed dev extension.

- If no dev extensions are installed, shows an error notification.
- If exactly one dev extension is installed, rebuilds it immediately.
- If multiple dev extensions are installed, opens a fuzzy picker to
select which one to rebuild.

Makes it easy for devs to trigger a rebuild with a keymap once an action
is defined with this PR.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- Added `RebuildDevExtension` action to rebuild installed dev extensions
from the command palette

<img width="675" height="310" alt="Screenshot 2026-04-29 at 1 49 54 AM"
src="https://github.com/user-attachments/assets/dbf618f7-f590-40aa-bc5c-580eea9f0001"
/>

<img width="623" height="329" alt="Screenshot 2026-04-29 at 1 50 16 AM"
src="https://github.com/user-attachments/assets/b4bb4131-924f-442b-8351-528a87698399"
/>

---------

Co-authored-by: MrSubidubi <finn@zed.dev>