- Adds `STORAGE_KEY_FILTERED_VIDEOS` and `MAX_PERSISTED_VIDEOS` constants.
- Implements `loadPersistedFilteredVideos` and `persistFilteredVideos` helper methods.
- Updates `loadVideos` to load persistent videos optimistically and emit "persistent-cache" updates.
- Ensures all persistent data is strictly re-filtered (blocked authors, NSFW, access control) before use.
- Skips emitting empty in-memory cache updates if optimistic data is available to prevent UI flashing.
- Persists fresh filtered results in `applyAndNotify` to keep cache up-to-date.
- Adds comprehensive verification script logic (tested via `scripts/verify-optimistic-cache.mjs` before cleanup).