feat: guest selections with per-person identity (#292)

Introduces a new "Per-guest selections" identity mode for event
feedback, letting each visitor register under their own name so their
likes/favorites/comments/ratings are tracked independently. Includes
admin insights (list, per-guest detail, aggregate view, export) and
advanced identity features (forget-me, email recovery, invite tokens,
merge).

New event-level setting
- event_feedback_settings.identity_mode = 'simple' | 'guest' (default
  'simple' → zero behavior change for existing events).
- Admin UI radio under Feedback Settings to toggle per event.

Root cause of the previous "all guests share state" bug
- generateGuestIdentifier() was sha256(ip + userAgent), so every visitor
  on the same WiFi + similar device collided into one identity.
- Now: when a verified guest JWT is present (x-guest-token header),
  req.guest.identifier takes precedence — per-person rate limits and
  per-person deduplication.

Phase 1 — identity layer
- Migration 078: new gallery_guests, guest_invites, guest_verification_
  codes tables; identity_mode column + check constraint; nullable
  guest_id FK on photo_feedback.
- New guest JWT type scoped to (eventId, guestId).
- New middleware guestAuth.resolveGuest (non-blocking) + requireGuest.
- POST /gallery/:slug/guest, GET /guest/me, DELETE /guest/me.
- Gallery feedback route enforces guest identity in guest mode and
  reads name/email from the verified token (never from the body).
- Frontend GuestIdentityContext + GuestNamePromptModal; axios
  interceptor injects x-guest-token on gallery API calls.
- Feedback-only blocking: gallery opens freely, prompt only on first
  interactive feedback action.
- Admin "Guests" tab (conditional on identity_mode='guest') with the
  AdminGuestsList component.

Phase 2 — admin insights
- GET /admin/events/:eventId/guests list + aggregated counts.
- GET /admin/events/:eventId/guests/:guestId detail with per-type
  groupings; AdminGuestDetail modal with thumbnail grid + tabs.
- GET /admin/events/:eventId/guests/aggregate sorted by distinct guest
  pick count; GuestSelectionsAggregate component.
- Per-guest export (txt/csv/json) and bulk export-all ZIP.

Phase 3 — polish
- 3.1 Self-service forget-me link in gallery footer.
- 3.2 Email-based identity recovery: POST /guest/recover sends a
  6-digit code via the existing emailProcessor, POST /guest/verify
  exchanges it for a token (rate-limited, enumeration-safe).
- 3.3 Admin invite tokens: pre-mint identities, share URLs with
  ?invite=, single-use redemption stripping the param from history.
- 3.4 Admin merge endpoint reassigns feedback + soft-deletes sources.

Shared helper
- useGalleryFeedbackAction hook wraps the identity-check logic for
  inline like buttons across Masonry/Grid/Justified/Mosaic/Carousel/
  Timeline/Premium layouts.

Backwards compatibility
- Existing events default to 'simple' after migration; behavior
  unchanged.
- Legacy photo_feedback rows keep guest_id NULL; admin shows them in
  the generic feedback moderation view as before.
- feedback_count denormalized stat now uses COALESCE(guest_id,
  guest_identifier) so per-guest counts are accurate without touching
  legacy rows.

Verified end-to-end against local Docker
- Migration clean on existing data.
- Simple mode unchanged (no prompt, legacy flow).
- Guest mode: Alice registers on click, tokens persist in
  sessionStorage, feedback rows carry guest_id.
- Carol via invite link auto-redeems, sees Alice's "1 likes" badge.
- Admin Guests tab shows both with correct counts; detail modal
  displays thumbnail grid with badges; aggregate view sorts by picker
  count (photo 227 = 2, others = 1); CSV/JSON export matches DB.
- Merge Carol into Alice: feedback reassigned, Carol soft-deleted,
  Alice count = 4.

frontend/src/hooks/useGalleryFeedbackAction.ts

@@ -0,0 +1,69 @@
+import { useCallback } from 'react';
+import { feedbackService } from '../services/feedback.service';
+import { useGuestIdentityOptional } from '../contexts/GuestIdentityContext';
+
+/**
+ * Shared helper used by gallery layout "quick action" buttons (like, favorite,
+ * rating, etc.) to submit feedback with proper identity handling:
+ *
+ *   - In guest identity mode: ensures the visitor has a guest token (prompts
+ *     if needed), then submits. Server reads name/email from the token.
+ *   - In simple mode with require_name_email: callers still need to show
+ *     their own inline FeedbackIdentityModal (we return `needsSimpleIdentity`
+ *     to signal this).
+ *   - In simple mode without require_name_email: submits directly.
+ */
+export function useGalleryFeedbackAction() {
+  const guestIdentity = useGuestIdentityOptional();
+
+  /**
+   * Submit a feedback action. Returns:
+   *   - { submitted: true } if the submission happened.
+   *   - { cancelled: true } if the user cancelled the guest prompt.
+   *   - { needsSimpleIdentity: true } if the caller must show its own legacy
+   *     identity modal (simple mode with require_name_email).
+   */
+  const submit = useCallback(
+    async (
+      slug: string,
+      photoId: number | string,
+      action: {
+        feedback_type: 'like' | 'favorite' | 'rating' | 'comment';
+        rating?: number;
+        comment_text?: string;
+      },
+      options?: {
+        requireNameEmail?: boolean;
+        savedIdentity?: { name: string; email: string } | null;
+      }
+    ): Promise<{ submitted?: boolean; cancelled?: boolean; needsSimpleIdentity?: boolean }> => {
+      if (guestIdentity?.identityMode === 'guest') {
+        try {
+          await guestIdentity.ensureIdentity();
+        } catch {
+          return { cancelled: true };
+        }
+        await feedbackService.submitFeedback(slug, String(photoId), action);
+        return { submitted: true };
+      }
+
+      // Simple mode
+      if (options?.requireNameEmail && !options.savedIdentity) {
+        return { needsSimpleIdentity: true };
+      }
+
+      await feedbackService.submitFeedback(slug, String(photoId), {
+        ...action,
+        guest_name: options?.savedIdentity?.name,
+        guest_email: options?.savedIdentity?.email,
+      });
+      return { submitted: true };
+    },
+    [guestIdentity]
+  );
+
+  return {
+    submit,
+    isGuestMode: guestIdentity?.identityMode === 'guest',
+  };
+}