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>