fix: prefer most specific file proxy match

[vagdotdev]

Summary

• prefer the longest matching file proxy prefix when multiple proxy patterns match
• keep database files taking precedence before proxy fallback
• add regression coverage for broad-first overlapping disk proxies

Validation

• bun test tests/routes/file-proxy04.test.ts
• bun test
• bunx tsc --noEmit
• bun run format:check
• bun run build
• git diff --check

/claim #5

[vagdotdev]

/claim #5