feat: restructure swiftpm layout, rc release flow, and perf tooling

[tankibaj]

Summary

• restructure runtime/build flow around SwiftPM server binary
• add RC prerelease workflow with automatic update of \
• split stable vs prerelease Homebrew channels
• harden version handling and formula/template sync
• add performance + smoke test scripts
• improve runtime logger to async queued writes with rotation support

Validation

• swift build -c release --product afm-api-server
• ./tests/completion_and_tool_calling.sh http://127.0.0.1:8000
• ./tests/function_call.sh http://127.0.0.1:8000
• RC workflow run passed and updated prerelease tap automatically