feat: persona onboarding — invite tokens, self-service setup, persona creation, switcher

New user flow:
  1. Admin: python manage_passwords.py invite <username>  → generates URL
  2. User visits /setup/<token> → sets own password → logged in
  3. User redirected to /setup/persona → fills name/emoji/description
  4. persona_template.py generates all starter files → lands at /{user}/{persona}

Multiple personas:
  - Header persona name is now a clickable dropdown listing all personas
  - "New persona" link at bottom → /setup/persona (available to logged-in users)
  - /api/personas endpoint returns persona list for current session user

New files:
  - persona_template.py: generates IDENTITY/SOUL/PROTOCOLS/USER/HELP.md + data files
  - routers/onboarding.py: /setup/{token}, /setup/persona GET+POST
  - static/setup.html: two-step form (password → persona), emoji picker, mobile-friendly

Updated:
  - auth_utils.py: create_invite(), validate_invite(), consume_invite()
  - manage_passwords.py: invite command with URL output
  - auth_middleware.py: /setup/* prefix is public (invite tokens need no auth)
  - routers/ui.py: /api/personas endpoint; post-login redirect if no personas
  - static/app.js: persona switcher dropdown with navigation + Add persona link
  - static/style.css: .persona-switcher, .persona-dropdown, mobile adjustments

Mobile: login/setup pages are card-centered with responsive padding;
dropdown avoids edge-clipping on narrow screens; logout button stays visible.

All 80 tests pass.

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
+from routers import ui, onboarding
 
 
 @asynccontextmanager
@@ -35,6 +35,9 @@ app.include_router(distill.router)
 app.include_router(auth.router)
 app.include_router(orchestrator.router)
 
+# Onboarding (invite tokens + persona creation — before ui.router)
+app.include_router(onboarding.router)
+
 # UI router (login + /{user}/{persona} — must be last to avoid swallowing API paths)
 app.include_router(ui.router)