fix(gallery): remove image file only after the delete commit succeeds (#2196)

delete_gallery_image() deleted the on-disk file before setting
is_active=False and committing. If that commit failed and rolled back,
the record stayed active but its file was already gone — a broken,
unviewable image (data loss).

Soft-delete and commit first, then remove the file best-effort, so a
missing or locked file can no longer 500 a delete that already succeeded
logically.

Adds tests/test_gallery_delete_file_ordering.py covering the
commit-failure (file kept) and success (file removed) paths.

routes/gallery_routes.py

@@ -931,15 +931,23 @@ def setup_gallery_routes() -> APIRouter:
                 raise HTTPException(404, "Image not found")
 
             img_filename = img.filename
-            # Remove the file from disk
-            img_path = _gallery_image_path(img_filename)
-            if img_path.exists():
-                img_path.unlink()
-
-            # Soft-delete the record
+            # Soft-delete the record first; the DB is the source of truth.
             img.is_active = False
             db.commit()
 
+            # Only after the soft-delete commit succeeds do we remove the file.
+            # If the file were deleted first and the commit then failed/rolled
+            # back, the still-active record would point at a missing file.
+            # Best-effort so a missing or locked file can't 500 a delete that
+            # already succeeded logically. Uses the path-confined resolver so a
+            # malformed stored filename can't escape generated_images.
+            try:
+                img_path = _gallery_image_path(img_filename)
+                if img_path.exists():
+                    img_path.unlink()
+            except Exception as e:
+                logger.warning(f"Could not remove gallery image file for {img_filename}: {e}")
+
             # Strip stale chat-history references so the image bubble
             # (and its prompt caption) doesn't come back after a server
             # reboot replays the session. We remove the matching tool