refactor: eliminate remaining panics and narrow platform types

- bin/types.ts: replace untyped PlatformMap with SupportedPlatform / TauriPlatform
- bin/helpers/merge.ts: narrow three platform maps to Record<SupportedPlatform, T>; assert supported platform at entry; guard linux/windows bundle with explicit errors
- bin/options/index.ts: inline the regex mapping now that PlatformMap is gone
- src-tauri/src/app/window.rs: swap Mutex<u32> for AtomicU32; harden web-url parse with map_err returning tauri::Error::Io
- src-tauri/src/app/setup.rs: downgrade tray icon panics to graceful fallback when no icon resolves