feat: add Windows Tauri tray MVP

[yyf0202]

Summary

• add cross-platform source registry foundation and structured cc_stats_web startup for desktop shells
• add a Tauri tray shell under desktop/cc-stats-tauri that launches, health-checks, restarts, and opens the Python web dashboard
• add Windows tray development notes and implementation docs while leaving macOS Swift UI unchanged

Test Plan

• python3 -m pytest tests -q -> 355 passed
• npm test -> 5 passed
• npm run build:web -> passed
• cargo test -> 8 passed
• cargo check -> passed

Notes

• macOS bundle artifacts were not committed; Windows packaging/runtime validation should continue on Windows.
• Statistics parsing/analyzing/pricing remains in Python; Tauri is only the platform shell.