Skills installation from URL has no content-type or size validation

[kumarabhirup]

Description

src/agents/skills-install.ts fetches skill files from URLs. The fetch likely doesn't validate:

• Content-Type header (could receive binary instead of markdown)
• Response size (could be a multi-GB file causing OOM)
• Content encoding (gzip bomb)

Impact

Low-Medium — A malicious skill URL could cause denial of service.

Suggested Fix

• Validate Content-Type is text/markdown or text/plain
• Enforce a maximum download size (e.g., 1MB)
• Stream the response and abort if size exceeds limit
• Validate the skill frontmatter after download