fix(logging): replace structlog with stdlib logging to prevent broken pipe crashes

structlog fails with BrokenPipeError when stdout is redirected (e.g., background
processes, Docker logs). Replace all structlog.get_logger() calls with
logging.getLogger() and convert keyword-style log calls to %-format strings.

Also removes stale Docs/tasks.md (2028 lines) and updates Robot Framework
tests to match current API behavior.

src/server/api/anime.py

@@ -455,11 +455,11 @@ async def trigger_rescan(
         }
     except AnimeServiceError as e:
         raise ServerError(
-            message=f"Rescan failed: {str(e)}"
+            message=str(e)
         ) from e
     except Exception as exc:
         raise ServerError(
-            message="Failed to start rescan"
+            message=f"Failed to start rescan: {exc}"
         ) from exc