feat(subagents): make subagent timeout configurable via config.yaml (#897)

* feat(subagents): make subagent timeout configurable via config.yaml

- Add SubagentsAppConfig supporting global and per-agent timeout_seconds
- Load subagents config section in AppConfig.from_file()
- Registry now applies config.yaml overrides without mutating builtin defaults
- Polling safety-net in task_tool is now dynamic (execution timeout + 60s buffer)
- Document subagents section in config.example.yaml
- Add make test command and enforce TDD policy in CLAUDE.md
- Add 38 unit tests covering config validation, timeout resolution, registry
  override behavior, and polling timeout formula

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(subagents): add logging for subagent timeout config and execution

- Log loaded timeout config (global default + per-agent overrides) on startup
- Log debug message in registry when config.yaml overrides a builtin timeout
- Include timeout in executor's async execution start log
- Log effective timeout and polling limit when a task is dispatched
- Fix UnboundLocalError: move max_poll_count assignment before logger.info

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ci(backend): add lint step and run all unit tests via Makefile

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix lint

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/config/app_config.py

@@ -11,6 +11,7 @@ from src.config.memory_config import load_memory_config_from_dict
 from src.config.model_config import ModelConfig
 from src.config.sandbox_config import SandboxConfig
 from src.config.skills_config import SkillsConfig
+from src.config.subagents_config import load_subagents_config_from_dict
 from src.config.summarization_config import load_summarization_config_from_dict
 from src.config.title_config import load_title_config_from_dict
 from src.config.tool_config import ToolConfig, ToolGroupConfig
@@ -87,6 +88,10 @@ class AppConfig(BaseModel):
         if "memory" in config_data:
             load_memory_config_from_dict(config_data["memory"])
 
+        # Load subagents config if present
+        if "subagents" in config_data:
+            load_subagents_config_from_dict(config_data["subagents"])
+
         # Load extensions config separately (it's in a different file)
         extensions_config = ExtensionsConfig.from_file()
         config_data["extensions"] = extensions_config.model_dump()