feat: account settings page + dedicated help page

- Add /settings page with password change form and personas list
- Add /help dedicated page (replaces help modal); renders HELP.md with
  collapsible sections, dark theme, back link to active persona
- Add 👤 account button and convert ? button to link in header
- Remove help modal HTML and ~55 lines of modal JS from main app
- Register settings and help routers in main.py

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

cortex/main.py

@@ -9,7 +9,7 @@ logging.basicConfig(level=logging.INFO, format="%(levelname)s:%(name)s: %(messag
 from config import settings
 from auth_middleware import SessionAuthMiddleware
 from routers import chat, google_chat, nextcloud_talk, files, distill, auth, orchestrator
-from routers import ui, onboarding
+from routers import ui, onboarding, settings, help
 
 
 @asynccontextmanager
@@ -42,6 +42,12 @@ app.mount("/static", StaticFiles(directory="static"), name="static")
 # Onboarding (invite tokens + persona creation — before ui.router)
 app.include_router(onboarding.router)
 
+# Account settings
+app.include_router(settings.router)
+
+# Help page
+app.include_router(help.router)
+
 # UI router (login + /{user}/{persona} — must be last to avoid swallowing API paths)
 app.include_router(ui.router)