Phase 6: rules editor + unsubscribe detection (AUD-72)

- FR-11 rules editor: plain-text area at /rules, saved and versioned
  (SaveRules appends a version; restore re-saves an old version), parse
  errors surfaced, one-click re-classify. The reply model now reads the
  rules document too (FR-11).
- FR-7 unsubscribe: parse and store List-Unsubscribe / List-Unsubscribe-Post
  (migration v6), detect email and web links (internal/unsubscribe), a
  domain-level ignore list, and an explicit record of what was marked. No
  code path contacts an unsubscribe link; acting on one needs Sam's approval.
- Migration v6 is additive; unsubscribe gains url/updated_at.
- Tests: detector, parser, store migration/records/candidates, rules editor,
  unsubscribe handlers, message-detail rendering.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/store/store.go

@@ -159,6 +159,25 @@ func (s *Store) applyMigrations(ctx context.Context) error {
 			return fmt.Errorf("record schema version 5: %w", err)
 		}
 	}
+	if version < 6 {
+		// Phase 6 (FR-7): store the raw List-Unsubscribe headers so detection
+		// runs without a refetch, and extend the unsubscribe tracker with the
+		// link it recorded and an update time.
+		for _, col := range []struct{ table, name, typ string }{
+			{"messages", "list_unsubscribe", "TEXT"},
+			{"messages", "list_unsubscribe_post", "TEXT"},
+			{"unsubscribe", "url", "TEXT NOT NULL DEFAULT ''"},
+			{"unsubscribe", "updated_at", "TEXT"},
+		} {
+			if err := s.ensureColumn(ctx, col.table, col.name, col.typ); err != nil {
+				return err
+			}
+		}
+		if _, err := s.db.ExecContext(ctx,
+			`INSERT OR IGNORE INTO schema_migrations (version) VALUES (6)`); err != nil {
+			return fmt.Errorf("record schema version 6: %w", err)
+		}
+	}
 	return nil
 }