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.

backend/src/utils/feedbackValidation.js

@@ -184,7 +184,9 @@ const validateFeedbackSettings = [
   body('allow_favorites').optional().isBoolean(),
   body('require_name_email').optional().isBoolean(),
   body('moderate_comments').optional().isBoolean(),
-  body('show_feedback_to_guests').optional().isBoolean()
+  body('show_feedback_to_guests').optional().isBoolean(),
+  body('identity_mode').optional().isIn(['simple', 'guest'])
+    .withMessage('identity_mode must be "simple" or "guest"')
 ];
 
 /**

backend/src/utils/tokenUtils.js

@@ -1,6 +1,7 @@
 const ADMIN_COOKIE_NAME = 'admin_token';
 const GALLERY_COOKIE_NAME = 'gallery_token';
 const GALLERY_COOKIE_PREFIX = 'gallery_token_';
+const GUEST_COOKIE_PREFIX = 'guest_token_';
 
 const DEFAULT_MAX_AGE_MS = 24 * 60 * 60 * 1000; // 24 hours
 
@@ -114,10 +115,37 @@ function getGalleryTokenFromRequest(req, slug) {
   return null;
 }
 
+function getGuestTokenFromRequest(req, slug) {
+  // Primary transport: custom header (set by frontend axios interceptor).
+  const headerToken = req.headers?.['x-guest-token'];
+  if (headerToken) {
+    return headerToken;
+  }
+
+  if (!req.cookies) {
+    return null;
+  }
+
+  if (slug) {
+    const cookieName = `${GUEST_COOKIE_PREFIX}${sanitizeSlugForCookie(slug)}`;
+    if (req.cookies[cookieName]) {
+      return req.cookies[cookieName];
+    }
+  }
+
+  const prefixed = Object.keys(req.cookies).find((name) => name.startsWith(GUEST_COOKIE_PREFIX));
+  if (prefixed) {
+    return req.cookies[prefixed];
+  }
+
+  return null;
+}
+
 module.exports = {
   ADMIN_COOKIE_NAME,
   GALLERY_COOKIE_NAME,
   GALLERY_COOKIE_PREFIX,
+  GUEST_COOKIE_PREFIX,
   sanitizeSlugForCookie,
   setAdminAuthCookie,
   clearAdminAuthCookie,
@@ -125,4 +153,5 @@ module.exports = {
   clearGalleryAuthCookies,
   getAdminTokenFromRequest,
   getGalleryTokenFromRequest,
+  getGuestTokenFromRequest,
 };