Persist detached Settings window size and position

[tsouth89]

Problem

The detached Settings window is built at 720×580 and centered, then the frontend forces it to 600×580 and recenters it on mount. Window events for non-main windows return before geometry persistence, so user size and position are lost on restart even though the geometry store models Settings.

Where

• apps/desktop-tauri/src-tauri/src/shell/settings_window.rs
• apps/desktop-tauri/src/Settings.tsx
• apps/desktop-tauri/src-tauri/src/main.rs
• apps/desktop-tauri/src-tauri/src/geometry_store.rs

Expected behavior

• Restore and persist the detached Settings window geometry.
• Clamp restored geometry to the current monitor work area.
• Use a single default size only for first run or invalid/missing geometry.
• Remove the mount-time forced resize/recenter after restoration.

Tests

Add focused Rust tests for stored/clamped Settings geometry and frontend coverage that the mount path does not overwrite a restored size.