feat: scan reads prompts embedded in videos; unreadable files no longer log errors

The output scan handed every .mp4 to Pillow and logged one ERROR per file.
ComfyUI's video savers store the queued graph as JSON in the container's
comment tag, so those files carry prompts worth linking.

- utils/video_metadata.py reads the comment/description tag through
  ffprobe with a timeout, normalised to the PNG text-chunk shape so the
  existing parser handles both; without ffprobe videos are skipped and a
  single INFO notice is logged
- _extract_comfyui_metadata routes videos there and logs unreadable images
  as warnings, since the scan carries on past them

Test hygiene: every aiohttp test base class overrode tearDownAsync without
calling super(), so no test client was ever closed. That produced thousands
of ResourceWarnings, "Unclosed client session" errors from asyncio that
broke log assertions, and doubled the suite's run time.

py/api/__init__.py

@@ -31,6 +31,7 @@ from .lora_integration import LoraIntegrationMixin
 try:
     from ...database.operations import PromptDatabase
     from ...utils.logging_config import get_logger
+    from ...utils.video_metadata import is_video_path, read_video_metadata
 except ImportError:
     import sys
 
@@ -39,6 +40,7 @@ except ImportError:
     )
     from database.operations import PromptDatabase
     from utils.logging_config import get_logger
+    from utils.video_metadata import is_video_path, read_video_metadata
 
 
 def _get_project_root():
@@ -665,16 +667,21 @@ class PromptManagerAPI(
         return []
 
     def _extract_comfyui_metadata(self, image_path):
-        """Extract ComfyUI workflow metadata from PNG image files."""
+        """Embedded ComfyUI metadata of an image (PNG text chunks) or a video.
+
+        Videos go through ffprobe (see utils/video_metadata). Unreadable files
+        are a warning, not an error: a scan over a large output tree meets
+        truncated and foreign files, and it carries on past them.
+        """
+        if is_video_path(image_path):
+            return read_video_metadata(image_path)
         try:
             with Image.open(image_path) as img:
-                metadata = {}
-                if hasattr(img, "text"):
-                    for key, value in img.text.items():
-                        metadata[key] = value
-                return metadata
+                return dict(getattr(img, "text", None) or {})
         except Exception as e:
-            self.logger.error(f"Error reading {image_path}: {e}")
+            self.logger.warning(
+                f"Unreadable image {os.path.basename(str(image_path))}: {e}"
+            )
             return {}
 
     def _parse_comfyui_prompt(self, metadata):