feat(events): default Guest Feedback ON via admin setting (#520)

@Rekoo-PS asked for an admin-level switch so new events can have Guest
Feedback enabled out of the box instead of toggling it on every time.
Mirrors the existing event_default_require_password pattern (#317) —
same shape end-to-end, same set of five files.

- publicSettings.js: whitelist + expose event_default_feedback_enabled
  (defaults to false to match the prior hard-coded form default; no
  behaviour change for existing installs until an admin flips it).
- adminEvents.js: rename `feedback_enabled = false` destructure to
  `feedback_enabled: feedbackEnabledInput` so we can distinguish
  "omitted" from "explicit false", then resolve the default from the
  setting only when the caller omitted it — identical to the
  require_password handling a few lines above.
- Frontend EventSettings type + state + loader: new boolean,
  default false.
- EventsTab: toggle UI right under "Require password by default".
- CreateEventPage: one-shot useEffect that seeds
  feedback_settings.feedback_enabled from the public setting on first
  load (mirrors the require_password seed effect right above it).
  Sub-toggles (likes / ratings / comments) keep their hard-coded
  true defaults so flipping the master setting immediately gives
  sensible behaviour without a second admin setting to manage.

Refs: #520

frontend/src/features/settings/hooks/useSettingsState.ts

@@ -54,6 +54,7 @@ export interface EventSettings {
   event_require_event_date: boolean;
   event_require_expiration: boolean;
   event_default_require_password: boolean;
+  event_default_feedback_enabled: boolean;
   gallery_show_filter_bar: boolean;
   event_phone_field_enabled: boolean;
 }
@@ -133,6 +134,7 @@ export function useSettingsState() {
     event_require_event_date: true,
     event_require_expiration: true,
     event_default_require_password: true,
+    event_default_feedback_enabled: false,
     gallery_show_filter_bar: true,
     event_phone_field_enabled: false
   });
@@ -220,6 +222,7 @@ export function useSettingsState() {
         event_require_event_date: toBoolean(settings.event_require_event_date, true),
         event_require_expiration: toBoolean(settings.event_require_expiration, true),
         event_default_require_password: toBoolean(settings.event_default_require_password, true),
+        event_default_feedback_enabled: toBoolean(settings.event_default_feedback_enabled, false),
         gallery_show_filter_bar: toBoolean(settings.gallery_show_filter_bar, true),
         event_phone_field_enabled: toBoolean(settings.event_phone_field_enabled, false)
       });