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/models/factory.py

@@ -1,4 +1,5 @@
 import logging
+
 from langchain.chat_models import BaseChatModel
 
 from src.config import get_app_config, get_tracing_config, is_tracing_enabled
@@ -6,6 +7,7 @@ from src.reflection import resolve_class
 
 logger = logging.getLogger(__name__)
 
+
 def create_chat_model(name: str | None = None, thinking_enabled: bool = False, **kwargs) -> BaseChatModel:
     """Create a chat model instance from the config.
 
@@ -50,9 +52,7 @@ def create_chat_model(name: str | None = None, thinking_enabled: bool = False, *
             )
             existing_callbacks = model_instance.callbacks or []
             model_instance.callbacks = [*existing_callbacks, tracer]
-            logger.debug(
-                f"LangSmith tracing attached to model '{name}' (project='{tracing_config.project}')"
-            )
+            logger.debug(f"LangSmith tracing attached to model '{name}' (project='{tracing_config.project}')")
         except Exception as e:
             logger.warning(f"Failed to attach LangSmith tracing to model '{name}': {e}")
     return model_instance