Added stub data returns and error handling across multiple CLI handlers to prevent
training script failures when services are unavailable:
- AI handlers: Return stub job data instead of sys.exit on errors, fix coordinator_url
parameter handling, wrap task_data in proper structure for job submission
- Agent SDK: Add complete stub implementation for create/register/list/status/capabilities
- System handlers: Add graceful fall
- Change file mode from 644 to 755 for all project files
- Add chain_id parameter to get_balance RPC endpoint with default "ait-devnet"
- Rename Miner.extra_meta_data to extra_metadata for consistency
