handbook alignment: profile.updated mirror, health contract, Synapse gateway ...

Handbook gaps closed (10-platform auth/health/notifications):

- webhooks: handle user.profile_updated — mirror the gnexus-auth profile
  into navi_users (name, contact fields, avatar_url — new column, boot
  migration); role/permissions keep their dedicated events
- auth: avatar_url now flows through the login upsert and the API-token
  resolution path
- /health: status is now the aggregate of the sub-checks (degraded embed
  or hive no longer reports plain ok); embed probe cached for 10 s; body
  grew the machine-readable checks{} map, legacy embed/hive payloads kept
- Synapse: s2s delivery gateway — POST /webhooks/synapse (both spellings),
  per-user delivery secrets (synapse_targets, Fernet-encrypted, shown
  once), verification via gnexus-synapse v0.1.2 client lib, idempotent
  event ids; deliveries are verified and logged for now — navi generates
  no outbound events by decision; web-push stays as the local browser
  channel
- webclient settings: Synapse deliveries panel (add/revoke targets)

Apply review fixes to API token auth system ...

Backend:
- navi/auth/deps.py: replace 3 DB round-trips with single JOIN query for
  token resolution; update last_used_at still separate (best-effort)
- navi/api/routes/api_tokens.py: replace asyncpg-specific "UPDATE 1"
  string check with RETURNING id fetchrow; increase token_prefix from
  8 to 12 chars for better visual identification; add security notes
- tests/unit/auth/test_api_tokens.py: update tests for JOIN query and
  RETURNING-based revoke

Frontend:
- webclient/src/components/settings/ShowTokenModal.vue: new modal that
  shows the plain token in a readonly field with copy button and
  explicit warning — replaces the transient toast notification
- webclient/src/components/settings/ApiKeysPanel.vue: use ShowTokenModal
- webclient/src/composables/useWebSocket.js: add security comment about
  localStorage XSS risk and query param log exposure

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

Add API token auth system for headless/micro clients ...

Backend:
- navi/auth/_ddl.py: add api_tokens table with boot-time migration
- navi/auth/deps.py: _resolve_user now falls back to X-Api-Token header
  and ?api_token query param for WebSocket auth
- navi/auth/__init__.py: add ApiToken pydantic model
- navi/api/routes/api_tokens.py: CRUD endpoints (POST/GET/DELETE)
- navi/main.py: wire api_tokens router

Frontend:
- webclient/src/App.vue: add #settings hash routing
- webclient/src/components/settings/: SettingsView, ApiKeysPanel,
  CreateKeyModal with copy-to-clipboard flow
- webclient/src/api/index.js: token CRUD API functions
- webclient/src/stores/apiTokens.js: Pinia store
- webclient/src/components/sidebar/AppSidebar.vue: settings link
- webclient/src/composables/useWebSocket.js: append ?api_token= when
  localStorage token is present

Tests:
- tests/unit/auth/test_api_tokens.py: 10 unit tests covering token
  resolution (header + query param), revoke, missing/revoked tokens,
  orphan users, and CRUD endpoints

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