test(recording): cover encoder and transport bounds

[yashranaway]

Progresses #36

Summary

• cover all 12 recording format/quality argument combinations through a controlled ffmpeg process
• make executable discovery inputs explicit and test relative, directory, non-executable, and valid candidates
• verify consecutive capture failures abort at the documented threshold and stop timeouts remain bounded
• prove capabilities match every protocol command and oversized raw socket requests never reach the handler

Verification

• CI-equivalent Swift 6.1 container: 39/39 protocol tests plus MCP integration passed
• npx --yes pnpm@9.15.0 test:runtime
• git diff --check