#12819: docs(hooks): document plugin hook names and clarify naming

## Summary Documents currently implemented plugin hook names and clarifies internal-hook vs plugin-hook naming to prevent confusion. ## What changed - Updated `docs/tools/plugin.md` (`Plugin hooks` section): - Added the currently available plugin hook names: - `before_agent_start`, `agent_end` - `message_received`, `message_sending`, `message_sent` - `before_tool_call`, `after_tool_call` - `session_start`, `session_end` - Added a naming note to use underscore hook names exactly (for example `message_received`, not `message:received`). - Updated `docs/automation/hooks.md`: - Renamed `Future Events` to `Future Events (internal hooks)` - Clarified that the listed `type:action` names belong to internal hooks - Added a note pointing readers to plugin hook names under `/tools/plugin#plugin-hooks` ## Why Issue #12436 reports confusion where plugin hooks appeared undocumented and `message:received` looked like a future-only event. The actual confusion is between two hook systems with different naming conventions (internal `type:action` vs plugin underscore names). This PR documents the available plugin hooks and disambiguates naming. Closes #12436 ## Contributing checklist - [x] AI-assisted: yes (prepared with OpenClaw assistant, model: `openai-codex/gpt-5.3-codex`) - [x] Testing level: lightly tested (docs-only change; link/build/test not run for this docs PR) - [x] Confirmed understanding of change and impact