fix: serve jpeg project favicons with image mime

[sabraman]

Summary

• add .jpeg to the favicon content-type map used by the project favicon proxy
• add a regression test covering a project icon discovered from HTML metadata

Why

The project favicon route resolves arbitrary rel="icon" hrefs from user projects. When a project used a .jpeg icon, the file could be found and served, but the response fell back to application/octet-stream instead of image/jpeg.

Verification

• bun run vitest apps/server/src/projectFaviconRoute.test.ts
• bun fmt
• bun lint
• bun typecheck

[sabraman]

Closing in favor of upstream PR pingdotgg#1313.