Cache theme colors and harden overlay retries

[Batchhh]

Summary

• Cache theme color lookups in src/ui/theme.rs so repeated access returns precomputed UIColor values instead of rebuilding them on every call.
• Switch several UI registries and feedback generators to parking_lot::Mutex and remove unnecessary .unwrap() locking in menu handling and rendering paths.
• Simplify a few animation/toast closures to reduce cloning noise and keep retained view references clearer.
• Harden overlay initialization in src/ui/window.rs with bounded retry attempts and exponential backoff before giving up.

Testing

• Not run.
• Reviewed the diff for overlay retry behavior to confirm retries are capped at 10 attempts and reset after a successful window fetch.
• Reviewed theme accessors to confirm each public getter now returns a cached static color value.
• Reviewed menu lock call sites to confirm they consistently use the updated mutex type and locking style.