Fix missing columns in navi_users: add boot-time ALTER TABLE migration ...

The navi_users table already existed on this deployment, so the updated
CREATE TABLE IF NOT EXISTS was a no-op. Run ALTER TABLE ADD COLUMN for
username, first_name, last_name, phone, birth_date, country, city, locale
if they are missing (checked via information_schema.columns).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Propagate user profile to LLM context via current_user_info ContextVar ...

- Extend User model: username, first_name, last_name, phone, birth_date,
  country, city, locale (all from gnexus-auth profile)
- navi_users DDL: add new profile columns
- auth/deps + auth/callback: populate new fields on upsert
- /auth/me: return all profile fields
- Add current_user_info ContextVar for full user profile propagation
- websocket + messages: set current_user_info before agent.run()
- run_ephemeral: inherit and restore current_user_info
- ContextBuilder: _user_context_msg() injects [User context] with name,
  email, location, locale, role into LLM system messages
- _security_policy_msg: reads user_id/role from ContextVar directly

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Fix DDL race condition and PostgreSQL syntax error on startup ...

- _ensure_auth_tables now uses raw asyncpg.connect instead of get_session_store,
  avoiding PgSessionStore._MIGRATE running before navi_users exists
- Move _ensure_auth_tables before ensure_tables in startup so navi_users is
  created before any foreign-key references
- Replace invalid "ADD CONSTRAINT IF NOT EXISTS" with DO $$ block for
  memory_facts_user_cat_key

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Multi-user auth via gnexus-auth OAuth + hybrid role/permission model ...

- Integrate gnexus-auth-client-py (GAuthClient) for OAuth flow, token refresh,
  and webhook parsing
- Add navi/auth/ package: User model, Fernet encryptor, client singleton,
  deps (get_current_user, require_admin, require_permission)
- New tables: navi_users, user_auth_sessions (auto-created on startup)
- Session/memory isolation by user_id with legacy NULL support
- Cookie-based auth proxy: /auth/login, /callback, /logout, /me
- Webhook receiver /webhooks/gnexus-auth handling user events, global logout,
  session revocation, role/permission changes
- Admin endpoints (/admin/*) gated by role + permissions
- Webclient auth store with isAdmin/hasPermission guards
- Admin-only profile filtering in /agents/profiles
- 200/200 tests passing

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>