docs: document kwargs.get("action") convention for plugin tool dispatch (colon-syntax)

## Summary Third-party plugin developers using `self.method` for colon-syntax dispatch (e.g., `todo_tool:create`) will find it is always `None`. The framework's `normalize_tool_request()` correctly parses colon-syntax into `tool_args["action"]`, but `agent.py` never passes this value to `self.method`. All core framework tools (`scheduler.py`, `skills_tool.py`) already use `kwargs.get("action")` instead of `self.method` for dispatch. This convention is not documented anywhere, leading to confusion for plugin developers. ## Evidence ### Framework code path 1. `helpers/extract_tools.py:38-41` — splits `tool_name:action` and puts action into `tool_args["action"]` 2. `agent.py:886` — `tool_method = None` (initialized, never updated from parsed action) 3. `agent.py:912` — passes `method=tool_method` (always `None`) to Tool constructor 4. `helpers/tool.py:22` — `self.method = method` (always `None`) ### Core tools using the convention ```python # tools/scheduler.py:26 action = kwargs.get("action") or tool.args.get("action") or "" # tools/skills_tool.py:95 kwargs.get("action") or self.args.get("action") or "" ``` ### What `self.method` is used for Only for logging/display in `helpers/tool.py:64-67` — formatting the heading string. Never for dispatch. ## Suggested Fix Add a note to the plugin development documentation (`_example` profile's tool documentation or `docs/developer/plugins.md`) stating: > **Colon-syntax tool dispatch:** When using `tool_name:action` syntax, the action is passed via `kwargs.get("action")`, not `self.method`. Use `kwargs.get("action") or self.method` for maximum compatibility. ## Impact - Third-party plugin developers encounter silently broken dispatch - No runtime error — tools just return "unknown method" or fall through - Discovery requires tracing framework source code