docs: comprehensive doc audit — sync all docs to current state

- MASTER.md: tool count 40→47, add proactive notifications + spawn_agent rows, date bump
- ROADMAP.md: mark local orchestrator/web push/proactive notifs/spawn_agent/web_read/session_read as done, date bump
- ARCH__CHANNELS.md: rewrite notification channel config section — all 4 channels, all triggers, on-demand endpoints
- ARCH__SYSTEM.md: update tools/ module list to include files, agents
- README.md: update LLM backends in architecture diagram, add browser push to channels table
- CLAUDE.md: add doc update checklist to Documentation Philosophy section

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

CLAUDE.md

@@ -185,6 +185,19 @@ Cortex is a no-black-box system. Docs must match reality — at all times.
 - **CLAUDE.md + ARCH__*.md are the developer contract:** Update them as the architecture evolves.
 - **Stale docs are bugs.** If you notice drift, fix it before moving on.
 
+### Doc update checklist (run after any significant change)
+
+| Doc | Update when |
+|---|---|
+| `CLAUDE.md` | New tool, channel, router, major design change, tool count |
+| `cortex/static/HELP.md` | Any user-visible feature — tools, settings, UI, API endpoints |
+| `documentation/TODO__Agents.md` | Mark completed items; add new planned work |
+| `documentation/MASTER.md` | New capability goes live; tool count changes |
+| `documentation/ROADMAP.md` | Phase items completed or added |
+| `documentation/ARCH__CHANNELS.md` | New channel, notification trigger, or scheduler job |
+| `documentation/ARCH__SYSTEM.md` | New module, router, or tools/ file |
+| `README.md` | Architecture diagram, channels table, or setup steps change |
+
 ---
 
 ## Adding a New Tool