Handle invalid URLs in content type detection

[hiSandog]

Summary:

• Return binary from detectContentType when URL parsing fails instead of throwing.
• Add regression coverage alongside the existing requiresYtdlp invalid-URL case.

Validation:

• ./node_modules/.bin/vitest run --project unit src/download/index.test.ts
• npm run typecheck
• git diff --check

Note: the first sandboxed vitest attempt failed because loopback server binding was denied with listen EPERM; rerunning the same test command with elevated permissions passed.