fix: add sam2_weights_filenames for download dialog

Add sam2_weights_filenames to __init__.py so check_model_exists()
works correctly for SAM2. This ensures the download warning dialog
appears before downloading SAM2 weights, consistent with other models.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: keejkrej

cellacdc/__init__.py

@@ -525,11 +525,18 @@ def printl(*objects, pretty=False, is_decorator=False, idx=1, **kwargs):
 ]
 
 segment_anything_weights_filenames = [
-    'sam_vit_h_4b8939.pth', 
-    'sam_vit_l_0b3195.pth', 
+    'sam_vit_h_4b8939.pth',
+    'sam_vit_l_0b3195.pth',
     'sam_vit_b_01ec64.pth'
 ]
 
+sam2_weights_filenames = [
+    'sam2.1_hiera_large.pt',
+    'sam2.1_hiera_base_plus.pt',
+    'sam2.1_hiera_small.pt',
+    'sam2.1_hiera_tiny.pt'
+]
+
 deepsea_weights_filenames = [
     'segmentation.pth', 
     'tracker.pth'