Fix: Remove episodes from missing list on download/rescan

- Update _update_series_in_db to sync missing episodes bidirectionally
- Add delete_by_series_and_episode method to EpisodeService
- Remove downloaded episodes from DB after successful download
- Clear anime service cache when episodes are removed
- Fix tests to use 'message' instead of 'detail' in API responses
- Mock DB operations in rescan tests

src/server/services/download_service.py

@@ -201,7 +201,58 @@ class DownloadService:
         except Exception as e:
             logger.error("Failed to delete from database: %s", e)
             return False
-    
+
+    async def _remove_episode_from_missing_list(
+        self,
+        series_key: str,
+        season: int,
+        episode: int,
+    ) -> bool:
+        """Remove a downloaded episode from the missing episodes list.
+        
+        Called when a download completes successfully to update the
+        database so the episode no longer appears as missing.
+        
+        Args:
+            series_key: Unique provider key for the series
+            season: Season number
+            episode: Episode number within season
+            
+        Returns:
+            True if episode was removed, False otherwise
+        """
+        try:
+            from src.server.database.connection import get_db_session
+            from src.server.database.service import EpisodeService
+            
+            async with get_db_session() as db:
+                deleted = await EpisodeService.delete_by_series_and_episode(
+                    db=db,
+                    series_key=series_key,
+                    season=season,
+                    episode_number=episode,
+                )
+                if deleted:
+                    logger.info(
+                        "Removed episode from missing list: "
+                        "%s S%02dE%02d",
+                        series_key,
+                        season,
+                        episode,
+                    )
+                    # Clear the anime service cache so list_missing
+                    # returns updated data
+                    try:
+                        self._anime_service._cached_list_missing.cache_clear()
+                    except Exception:
+                        pass
+                return deleted
+        except Exception as e:
+            logger.error(
+                "Failed to remove episode from missing list: %s", e
+            )
+            return False
+
     async def _init_queue_progress(self) -> None:
         """Initialize the download queue progress tracking.
         
@@ -885,6 +936,13 @@ class DownloadService:
                 # Delete completed item from database (status is in-memory)
                 await self._delete_from_database(item.id)
                 
+                # Remove episode from missing episodes list in database
+                await self._remove_episode_from_missing_list(
+                    series_key=item.serie_id,
+                    season=item.episode.season,
+                    episode=item.episode.episode,
+                )
+                
                 logger.info(
                     "Download completed successfully: item_id=%s", item.id
                 )