Optimize scan process with quick/deep modes and archive tag merging

Quick scan (default):
- Pre-load all ImportTask records for O(1) duplicate checks
- Batch task creation commits (50 at a time)
- Cache import settings (5-min TTL)
- Skip pHash comparison for speed

Deep scan (on-demand):
- Full reprocessing of all files
- pHash similarity detection
- Optional thumbnail regeneration
- Optional sidecar re-application

Archive tag merging:
- Add archive tags to existing images when duplicates found
- Works for both hash and pHash duplicate detection

Also fixes:
- Add missing source/post tag icons to gallery templates

app/main.py

@@ -1114,20 +1114,51 @@ def delete_filtered_images():
 def trigger_import_celery():
     """
     Trigger a directory scan and import via Celery.
-    Replaces the old flag-file mechanism.
+
+    Supports two modes:
+    - Quick scan (default): Fast O(1) duplicate detection using pre-loaded lookups.
+      Only queues truly new files. Skips pHash comparison for speed.
+    - Deep scan: Full reprocessing of all files. Re-extracts metadata,
+      runs pHash comparison, optionally regenerates thumbnails and re-applies sidecars.
+
+    POST params:
+        source_dir: Source directory (default: /import)
+        dest_dir: Destination directory (default: /images)
+        deep: Set to 'true' for deep scan mode
+        regenerate_thumbnails: For deep scan, regenerate all thumbnails (default: true)
+        reapply_sidecars: For deep scan, re-apply sidecar metadata (default: true)
+        verify_hashes: For deep scan, verify content hashes (default: true)
     """
     try:
-        from app.tasks.scan import scan_directory
+        from app.tasks.scan import scan_directory, deep_scan_directory
 
         source_dir = request.form.get('source_dir', '/import')
         dest_dir = request.form.get('dest_dir', '/images')
+        is_deep = request.form.get('deep', 'false').lower() == 'true'
 
-        result = scan_directory.delay(source_dir, dest_dir)
+        if is_deep:
+            # Deep scan with full reprocessing
+            regenerate_thumbnails = request.form.get('regenerate_thumbnails', 'true').lower() == 'true'
+            reapply_sidecars = request.form.get('reapply_sidecars', 'true').lower() == 'true'
+            verify_hashes = request.form.get('verify_hashes', 'true').lower() == 'true'
+
+            result = deep_scan_directory.delay(
+                source_dir, dest_dir,
+                regenerate_thumbnails=regenerate_thumbnails,
+                reapply_sidecars=reapply_sidecars,
+                verify_hashes=verify_hashes
+            )
+            message = 'Deep import scan started'
+        else:
+            # Quick scan with optimized lookups
+            result = scan_directory.delay(source_dir, dest_dir)
+            message = 'Quick import scan started'
 
         return jsonify({
             'ok': True,
             'task_id': result.id,
-            'message': 'Import scan started'
+            'message': message,
+            'mode': 'deep' if is_deep else 'quick'
         })
     except Exception as e:
         return jsonify({'ok': False, 'error': str(e)}), 500