feat: engine/model in audit log + docs update

- tool_audit: ContextVars (engine, model) set at orchestrator run start; fields added to every entry
- orchestrator_engine: tool_audit.set_context("gemini", model_name) at run() start
- openai_orchestrator: tool_audit.set_context("openai", model label) at run() start
- audit table: Model column between Status and Args
- HELP.md: push notifications section, audit log in Files section, tool count 30→40, new API endpoints
- TODO__Agents.md: web_push and audit log marked complete with full detail

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

cortex/static/style.css

@@ -1261,7 +1261,8 @@
         .at-time   { width: 7em;  color: var(--muted); white-space: nowrap; }
         .at-tool   { width: 11em; color: var(--accent); font-weight: 500; }
         .at-status { width: 4.5em; font-weight: 600; }
-        .at-args   { width: 30%; color: var(--muted); }
+        .at-model  { width: 10em; color: var(--muted); }
+        .at-args   { width: 25%; color: var(--muted); }
         .at-result { color: var(--muted); }
         .at-status.ok     { color: #4ade80; }
         .at-status.error  { color: #f87171; }