feat: smart thumbnail cleanup and rename-aware file tracking

Delete thumbnails alongside DB rows in all three removal paths (watcher
detect, delete-from-disk command, remove-folder command) so orphans no
longer accumulate passively.

Intercept RenameMode::Both watcher events and handle them as in-place
path updates: renames the thumbnail file to the new hash and updates the
DB row without touching the embedding, avoiding a full rebuild on move.
Falls back to thumbnail regeneration if the file rename fails.

src-tauri/src/lib.rs

@@ -74,7 +74,7 @@ pub fn run() {
             // indexer::start_caption_worker(app.handle().clone(), pool.clone(), app_dir.clone());
             indexer::start_tagging_worker(app.handle().clone(), pool.clone(), app_dir.clone());
 
-            let watcher_handle = indexer::start_watcher(app.handle().clone(), pool.clone());
+            let watcher_handle = indexer::start_watcher(app.handle().clone(), pool.clone(), thumb_dir.clone());
 
             app.manage(pool);
             app.manage(media_tools);