feat: inline unsubscribe button on email rows

- ✉✕ button appears on rows where the email has a List-Unsubscribe header
- One-click POST / HTTP GET executed automatically; shows ✓ on success
- mailto: targets open the user mail client (we never auto-send email)
- POST /email/{id}/unsubscribe: detects sender, then processes — UserId scoped
- EmailSummaryDto gains IsStarred, HasListUnsubscribe, SupportsOneClick fields
- Both SearchService and CleanupService updated to populate new DTO fields

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

frontend/src/api/client.js

@@ -105,6 +105,7 @@ export const EmailApi = {
   unstar:     (id) => api.post(`/email/${id}/unstar`),
   trash:      (id) => api.post(`/email/${id}/trash`),
   untrash:    (id) => api.post(`/email/${id}/untrash`),
+  unsubscribe:(id) => api.post(`/email/${id}/unsubscribe`).then((r) => r.data),
 };
 
 export const ExportApi = {