feat(slideshow): admin ui for live slideshow

- per-event Live Slideshow card on the event detail page: generate/copy/
  regenerate/disable the share link + live style (transition, timing, color
  filter, watermark).
- shared SlideshowStyleFields, reused by the per-event card and the per-event-
  type preset section in the Edit Event Type modal.
- global watermark default card on the Event Types page (Settings -> slideshow).
- WatermarkSourcePicker: visible logo tiles with previews (light logo / dark-mode
  logo / favicon / event logo) instead of a blind dropdown.
- watermark mode tri-state (inherit/on/off) + white-vs-original style.
- supporting service methods + Event/EventType types.

frontend/src/services/eventTypes.service.ts

@@ -4,6 +4,7 @@
  */
 
 import { api } from '../config/api';
+import type { SlideshowStyle } from './slideshow.service';
 
 export interface EventType {
   id: number;
@@ -12,6 +13,9 @@ export interface EventType {
   emoji: string;
   theme_preset: string;
   theme_config: string | null;
+  // Live Slideshow preset new events of this type inherit (migration 138).
+  // Stored as a JSON string by the API; null = no preset.
+  slideshow_preset: string | null;
   display_order: number;
   is_system: boolean;
   is_active: boolean;
@@ -25,6 +29,7 @@ export interface CreateEventTypeData {
   emoji?: string;
   theme_preset?: string;
   theme_config?: Record<string, unknown>;
+  slideshow_preset?: SlideshowStyle | null;
   display_order?: number;
 }
 
@@ -34,6 +39,7 @@ export interface UpdateEventTypeData {
   emoji?: string;
   theme_preset?: string;
   theme_config?: Record<string, unknown>;
+  slideshow_preset?: SlideshowStyle | null;
   display_order?: number;
   is_active?: boolean;
 }

frontend/src/services/events.service.ts

@@ -138,6 +138,36 @@ export const eventsService = {
     await api.delete(`/admin/events/${id}`);
   },
 
+  // Live Slideshow ("Diashow") — mint/rotate the share token (admin)
+  async generateSlideshowLink(id: number): Promise<{ show_share_token: string; slideshow_url: string }> {
+    const response = await api.post(`/admin/events/${id}/slideshow/generate`);
+    return response.data;
+  },
+
+  // Disable the slideshow link (null the token) (admin)
+  async disableSlideshowLink(id: number): Promise<void> {
+    await api.post(`/admin/events/${id}/slideshow/disable`);
+  },
+
+  // Update live slideshow settings (display time / transition / style) (admin)
+  async updateSlideshowSettings(
+    id: number,
+    settings: {
+      show_interval_ms?: number;
+      show_transition?: string;
+      show_transition_ms?: number;
+      show_watermark?: boolean | null;
+      show_watermark_source?: string;
+      show_watermark_position?: string;
+      show_watermark_opacity?: number;
+      show_watermark_style?: string;
+      show_colorfilter?: string;
+    }
+  ): Promise<Record<string, unknown>> {
+    const response = await api.patch(`/admin/events/${id}/slideshow`, settings);
+    return response.data;
+  },
+
   // Force archive event (admin)
   async archiveEvent(id: number): Promise<void> {
     await api.post(`/admin/events/${id}/archive`);

frontend/src/services/settings.service.ts

@@ -189,11 +189,16 @@ export const settingsService = {
   },
 
   // Get settings by type
-  async getSettingsByType(type: 'branding' | 'theme' | 'general'): Promise<Record<string, any>> {
+  async getSettingsByType(type: 'branding' | 'theme' | 'general' | 'slideshow'): Promise<Record<string, any>> {
     const response = await api.get<Record<string, any>>(`/admin/settings/${type}`);
     return response.data;
   },
 
+  // Update global Live Slideshow defaults (watermark)
+  async updateSlideshowDefaults(settings: Record<string, unknown>): Promise<void> {
+    await api.put('/admin/settings/slideshow', settings);
+  },
+
   // Update branding settings
   async updateBranding(settings: BrandingSettings): Promise<void> {
     await api.put('/admin/settings/branding', settings);