feat(pai-voice-system): Add Linux support and CLI configuration

[sti0]

Summary

• Re-Adds full Linux platform support for the voice server (audio playback + notifications)
• Adds CLI arguments for runtime configuration (--port, --extra-args)
• Enhances .env loading from $PAI_DIR/.env with quote stripping (closes #346 )
• Adds devcontainer/PulseAudio documentation for containerized development

Changes

Linux Audio Support

• Auto-detects mpg123 or mpv for audio playback on Linux
• Falls back gracefully if no player is installed
• macOS continues to use built-in afplay

Linux Notifications

• Uses notify-send for desktop notifications on Linux
• macOS continues to use osascript

CLI Arguments

• --port / -p: Override server port
• --extra-args: Pass extra arguments to audio player (e.g., -o pulse for PulseAudio)

Environment Variables

• PAI_VOICE_SERVER_PORT: Server port (default: 8888)
• PAI_VOICE_SERVER_EXTRA_ARGS: Extra audio player arguments
• Enhanced .env parsing with quote stripping for values

Documentation

• Added devcontainer setup guide for PulseAudio
• Updated platform status to show Linux as fully supported
• Added changelog entry for v1.1.0

Test Plan

• [x] Voice notification plays on Linux with mpg123
• [x] CLI --port argument works
• [x] CLI --extra-args argument passes to audio player
• [x] .env values with quotes are parsed correctly
• [x] TypeScript compiles without errors