fix(Backend): Gravity Bridge response extraction & bot exception crash loop

* Restore step.content.parts traversal missing in prior bugfix
* Catch wide exceptions in bot.py chat_snapshot_scanner and move broken files to .json.failed to prevent loop aborts blocking the pending queue

bot.py

@@ -1381,8 +1381,12 @@ class GravityBot(commands.Bot):
                                     logger.error(f"[SNAPSHOT] Discord send failed for {project}: {e}")
 
                     f.unlink()  # Cleanup
-                except (json.JSONDecodeError, OSError) as e:
+                except Exception as e:
                     logger.warning(f"Bad chat snapshot {f.name}: {e}")
+                    try:
+                        f.rename(f.with_suffix('.json.failed'))
+                    except OSError:
+                        pass
         except Exception as e:
             logger.error(f"Error scanning chat snapshots: {e}")