feat(app): add custom protocol output directory

[pasrom]

Summary

• Add configurable output directory in Settings (defaults to ~/Downloads/MeetingTranscriber)
• Organize output into protocols/ (.md, .txt) and recordings/ (.wav) subdirectories
• Move audio files to output directory after processing
• Fix App Store entitlements to apply without notarization

Structure

~/Downloads/MeetingTranscriber/
├── protocols/
│   ├── 20260317_2130_meeting.md
│   └── 20260317_2130_meeting.txt
└── recordings/
    ├── 20260317_2130_meeting_mix.wav
    ├── 20260317_2130_meeting_app.wav
    └── 20260317_2130_meeting_mic.wav

Test plan

• Verify default output directory is ~/Downloads/MeetingTranscriber
• Change output directory in Settings, verify files go to new location
• Process audio file, verify .md/.txt in protocols/ and .wav in recordings/
• Verify "Open Protocols Folder" opens the root output directory
• App Store build: verify sandbox entitlements work with file picker