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/styles.css

@@ -256,6 +256,8 @@ input, select { background: var(--panel-2); border: 1px solid #2c3550; color: va
 .action-btn--danger:hover { color: var(--danger); }
 .email-row:hover .action-btn { opacity: 0.6; }
 .email-row--acting { opacity: 0.6; pointer-events: none; }
+.action-btn--unsub { font-size: 11px; }
+.action-btn--done { opacity: 1 !important; color: var(--ok); }
 
 .fv-sentinel { height: 1px; }
 .fv-loading-more { color: var(--muted); font-size: 13px; padding: 16px 0; text-align: center; }