feat: add Gitea Actions workflow to run agent YAMLs via AgentBackend API
- .gitea/workflows/run-agent.yml: workflow_dispatch with yaml_path input;
runs a specified agent YAML through upload-agent + SSE (SKILL.md §0.6 path A)
- scripts/run_agent_api.py: SSE runner with auto-confirm on stage_complete
(with retry), stage_error -> cancel + fail, reconnect on drops,
--max-runtime guard under the 3h Gitea/act_runner task caps,
SIGTERM-safe session cancellation, events.jsonl/final_output/summary artifacts
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>