Add application logging, SMTP email notifications, and supporting changes

Phase 5.4 — Application Logging:
- AppLog model + migration 0010 for unified audit/usage/error logging
- Usage logging middleware in app.py (after_request for /api/* requests)
- Error logging in 500 handler with traceback capture
- Audit logging for auth events (register, login, login_failed, logout,
  password_change) and admin actions (backup, restore, user_delete,
  registration_toggle, smtp_config, smtp_test)
- Admin log viewer (LogsView.vue) with stats, category/search/date
  filters, paginated table with expandable detail rows
- Admin logs API endpoints in admin.py (GET /logs, GET /logs/stats)
- Configurable retention via LOG_RETENTION_DAYS with hourly cleanup

Phase 5.5 — SMTP Email Notifications:
- aiosmtplib dependency for async email sending
- Email service (services/email.py) with STARTTLS/implicit TLS support
- Notification service (services/notifications.py) for security alerts
  and task due date reminders with per-user preferences
- Admin SMTP config endpoints (GET/PUT /api/admin/smtp, POST test)
- SMTP config in Config class with env var + Docker secret support
- Settings UI: notification preferences for all users, SMTP config
  section for admin with test email

Other changes:
- stream_chat() now accepts optional options dict (for num_predict)
- Increase assist MAX_BODY_CHARS from 3000 to 8000
- get_user_by_username() added to auth service
- apiStreamPost buffer processing refactored for robustness
- AppHeader: admin Logs nav link
- Router: /admin/logs route

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

src/fabledassistant/config.py

@@ -27,3 +27,13 @@ class Config:
     SECRET_KEY: str = _read_secret("SECRET_KEY", "SECRET_KEY_FILE", "dev-secret-change-me")
     SECURE_COOKIES: bool = os.environ.get("SECURE_COOKIES", "").lower() in ("1", "true", "yes")
     LOG_LEVEL: str = os.environ.get("LOG_LEVEL", "INFO")
+    LOG_RETENTION_DAYS: int = int(os.environ.get("LOG_RETENTION_DAYS", "90"))
+
+    # SMTP defaults (overridden by DB settings when configured via admin UI)
+    SMTP_HOST: str = os.environ.get("SMTP_HOST", "")
+    SMTP_PORT: int = int(os.environ.get("SMTP_PORT", "587"))
+    SMTP_USERNAME: str = os.environ.get("SMTP_USERNAME", "")
+    SMTP_PASSWORD: str = _read_secret("SMTP_PASSWORD", "SMTP_PASSWORD_FILE", "")
+    SMTP_FROM_ADDRESS: str = os.environ.get("SMTP_FROM_ADDRESS", "")
+    SMTP_FROM_NAME: str = os.environ.get("SMTP_FROM_NAME", "Fabled Assistant")
+    SMTP_USE_TLS: bool = os.environ.get("SMTP_USE_TLS", "true").lower() in ("1", "true", "yes")