Closes #58046 
Closes AI-353

Skills with descriptions over the 1024-byte limit now load with a
warning instead of failing. The warning appears in the thread footer
with clickable skill file rows, and the skill picker keeps the skill
icon while showing a right-aligned warning badge whose hover text
explains the issue.

Warning for single out-of-spec skill
<img width="2790" height="870" alt="image"
src="https://github.com/user-attachments/assets/f454b55a-8e05-438e-b4ff-356259ff6843"
/>

Warning for multiple out-of-spec skills
<img width="2796" height="646" alt="image"
src="https://github.com/user-attachments/assets/a0808cdd-4857-4a6b-a26e-15156afbffe9"
/>

Skill selection popup
<img width="1234" height="1118" alt="image"
src="https://github.com/user-attachments/assets/5bb463f6-7adb-4e39-8522-e322bf078aff"
/>

Skill management in settings
<img width="1768" height="1390" alt="image"
src="https://github.com/user-attachments/assets/85c6b179-e268-4518-8ca7-c73b55f92355"
/>


Release Notes:

- Allow loading skills whose descriptions exceed the 1024-byte limit by
showing warnings instead of failing to load them.

---------

Co-authored-by: Martin Ye <martin@zed.dev>
Co-authored-by: zed-zippy[bot] <234243425+zed-zippy[bot]@users.noreply.github.com>