feat(slideshow): add image fit setting (fill vs black bars)

object-fit was hardcoded to 'cover', which crops portrait photos heavily. Add a
global `slideshow_fit` setting (Settings -> Slideshow): 'cover' fills + crops,
'contain' shows the whole image with black bars (no crop). Default 'cover'
(unchanged). Stored in app_settings (no migration), resolved server-side into
the slideshow settings + /state poll so a running projector picks it up live.

frontend/src/components/admin/SlideshowGlobalDefaultsCard.tsx

@@ -16,11 +16,13 @@ import { settingsService } from '../../services/settings.service';
 import {
   SLIDESHOW_WATERMARK_POSITIONS,
   SLIDESHOW_WATERMARK_STYLES,
+  SLIDESHOW_FITS,
   type SlideshowGlobalDefaults,
 } from '../../services/slideshow.service';
 import { WatermarkSourcePicker } from './WatermarkSourcePicker';
 
 const DEFAULTS: SlideshowGlobalDefaults = {
+  slideshow_fit: 'cover',
   slideshow_watermark_enabled: false,
   slideshow_watermark_source: 'logo',
   slideshow_watermark_position: 'bottom-right',
@@ -43,6 +45,7 @@ export const SlideshowGlobalDefaultsCard: React.FC = () => {
     settingsService.getSettingsByType('slideshow').then((s) => {
       if (cancelled || !s) return;
       setVal({
+        slideshow_fit: s.slideshow_fit ?? DEFAULTS.slideshow_fit,
         slideshow_watermark_enabled: s.slideshow_watermark_enabled ?? DEFAULTS.slideshow_watermark_enabled,
         slideshow_watermark_source: s.slideshow_watermark_source ?? DEFAULTS.slideshow_watermark_source,
         slideshow_watermark_position: s.slideshow_watermark_position ?? DEFAULTS.slideshow_watermark_position,
@@ -70,13 +73,33 @@ export const SlideshowGlobalDefaultsCard: React.FC = () => {
     <Card padding="md" className="mb-6">
       <h2 className="text-lg font-semibold text-neutral-900 dark:text-neutral-100 mb-1 flex items-center gap-2">
         <MonitorPlay className="w-5 h-5" />
-        {t('slideshow.globalTitle', 'Global slideshow watermark')}
+        {t('slideshow.globalTitle', 'Global slideshow settings')}
       </h2>
       <p className="text-xs text-neutral-500 dark:text-neutral-400 mb-4">
-        {t('slideshow.globalDescription', 'Default logo watermark for every slideshow. Individual events can override this on or off.')}
+        {t('slideshow.globalDescription', 'Defaults for every slideshow. Events can override the watermark on or off.')}
       </p>
 
       <div className="space-y-4">
+        {/* Image fit */}
+        <div>
+          <label className={labelClass}>{t('slideshow.fitLabel', 'Image fit')}</label>
+          <select
+            value={val.slideshow_fit}
+            onChange={(e) => setVal({ ...val, slideshow_fit: e.target.value as SlideshowGlobalDefaults['slideshow_fit'] })}
+            className={inputClass}
+          >
+            {SLIDESHOW_FITS.map((f) => (
+              <option key={f} value={f}>
+                {t(`slideshow.fit.${f}`, f === 'contain' ? 'Black bars (no crop)' : 'Fill screen (crop)')}
+              </option>
+            ))}
+          </select>
+          <p className="text-xs text-neutral-500 dark:text-neutral-400 mt-1">
+            {t('slideshow.fitHint', '"Fill" crops to fill the screen; "Black bars" shows the whole photo — better for portrait images.')}
+          </p>
+        </div>
+
+        <div className="pt-2 border-t border-neutral-200 dark:border-neutral-700">
         <label className="flex items-start gap-2">
           <input
             type="checkbox"
@@ -159,6 +182,7 @@ export const SlideshowGlobalDefaultsCard: React.FC = () => {
             </div>
           </div>
         )}
+        </div>
 
         <Button variant="outline" size="md" leftIcon={<Save className="w-4 h-4" />} onClick={save} isLoading={saving}>
           {t('common.save', 'Save')}

frontend/src/i18n/locales/de.json

@@ -3206,8 +3206,14 @@
       "on": "An",
       "off": "Aus"
     },
-    "globalTitle": "Globales Diashow-Wasserzeichen",
-    "globalDescription": "Standard-Logo-Wasserzeichen für jede Diashow. Einzelne Events können es überschreiben (an/aus).",
+    "globalTitle": "Globale Diashow-Einstellungen",
+    "globalDescription": "Vorgaben für jede Diashow. Events können das Wasserzeichen überschreiben (an/aus).",
+    "fitLabel": "Bildanpassung",
+    "fit": {
+      "cover": "Bildschirm füllen (beschneiden)",
+      "contain": "Schwarze Balken (kein Beschnitt)"
+    },
+    "fitHint": "„Füllen“ beschneidet das Bild zum Ausfüllen; „Schwarze Balken“ zeigt das ganze Foto – besser für Hochformat.",
     "defaultsSaved": "Diashow-Vorgaben gespeichert",
     "liveHint": "Änderungen werden in einer laufenden Diashow innerhalb weniger Sekunden übernommen – der Link muss nicht neu erstellt werden.",
     "saveSettings": "Diashow-Einstellungen speichern",

frontend/src/i18n/locales/en.json

@@ -3230,8 +3230,14 @@
       "on": "On",
       "off": "Off"
     },
-    "globalTitle": "Global slideshow watermark",
-    "globalDescription": "Default logo watermark for every slideshow. Individual events can override this on or off.",
+    "globalTitle": "Global slideshow settings",
+    "globalDescription": "Defaults for every slideshow. Events can override the watermark on or off.",
+    "fitLabel": "Image fit",
+    "fit": {
+      "cover": "Fill screen (crop)",
+      "contain": "Black bars (no crop)"
+    },
+    "fitHint": "\"Fill\" crops to fill the screen; \"Black bars\" shows the whole photo — better for portrait images.",
     "defaultsSaved": "Slideshow defaults saved",
     "liveHint": "Changes apply to a running slideshow within a few seconds — no need to regenerate the link.",
     "saveSettings": "Save slideshow settings",

frontend/src/pages/gallery/SlideshowPage.tsx

@@ -13,6 +13,7 @@ const DEFAULT_SETTINGS: SlideshowSettings = {
   transition: 'crossfade',
   transition_ms: 800,
   colorfilter: 'none',
+  fit: 'cover',
   watermark: null,
 };
 
@@ -210,6 +211,7 @@ export function SlideshowPage() {
           transition: state.transition,
           transition_ms: state.transition_ms,
           colorfilter: state.colorfilter,
+          fit: state.fit,
           watermark: state.watermark,
         };
         if (JSON.stringify(next) !== JSON.stringify({
@@ -217,6 +219,7 @@ export function SlideshowPage() {
           transition: prev.transition,
           transition_ms: prev.transition_ms,
           colorfilter: prev.colorfilter,
+          fit: prev.fit,
           watermark: prev.watermark,
         })) {
           setSettings(next);
@@ -288,13 +291,13 @@ export function SlideshowPage() {
   const imgStyle = (buf: 0 | 1): React.CSSProperties => {
     const isActive = active === buf;
     const style: React.CSSProperties = {
-      // Fill the whole viewport. `maxWidth/maxHeight` alone left the <img> at
-      // the photo's intrinsic size (e.g. the 1920px preview), so it never
-      // scaled up to the projector — leaving black bars all round. Pin to the
-      // full container and let object-fit do the scaling.
+      // Pin to the full viewport (maxWidth/maxHeight alone left the <img> at the
+      // photo's intrinsic ≤1920px size, so it never scaled up to the projector).
+      // `fit` decides the rest: 'cover' fills + crops, 'contain' letterboxes the
+      // whole image with black bars (no crop — kinder to portrait photos).
       width: '100%',
       height: '100%',
-      objectFit: 'cover',
+      objectFit: settings.fit === 'contain' ? 'contain' : 'cover',
       filter: imageFilter(settings.colorfilter),
     };
     if (settings.transition === 'kenburns' && isActive) {

frontend/src/services/slideshow.service.ts

@@ -2,6 +2,10 @@ import { api } from '../config/api';
 
 export type SlideshowTransition = 'crossfade' | 'cut' | 'slide' | 'kenburns' | 'dipwhite' | 'dipblack';
 export type SlideshowColorFilter = 'none' | 'bw' | 'sepia' | 'warm' | 'cool' | 'vignette';
+// How each slide fills the screen: 'cover' = fill, crop to aspect; 'contain' =
+// whole image with black bars (no crop — best for mixed portrait/landscape).
+export type SlideshowFit = 'cover' | 'contain';
+export const SLIDESHOW_FITS: SlideshowFit[] = ['cover', 'contain'];
 // Which logo the watermark overlays. The first three are branding assets the
 // admin uploads in Settings → Branding; 'event' is the event's own hero logo.
 export type SlideshowWatermarkSource = 'logo' | 'logo_dark' | 'favicon' | 'event';
@@ -47,6 +51,8 @@ export const DEFAULT_SLIDESHOW_STYLE: SlideshowStyle = {
 // truth for the watermark look; the per-event watermark mode 'inherit'/'on'
 // renders with exactly these.
 export interface SlideshowGlobalDefaults {
+  // How slides fill the screen (fill+crop vs letterbox/black bars).
+  slideshow_fit: SlideshowFit;
   slideshow_watermark_enabled: boolean;
   slideshow_watermark_source: SlideshowWatermarkSource;
   slideshow_watermark_position: SlideshowWatermarkPosition;
@@ -70,6 +76,7 @@ export interface SlideshowSettings {
   transition: SlideshowTransition;
   transition_ms: number;
   colorfilter: SlideshowColorFilter;
+  fit: SlideshowFit;
   watermark: SlideshowWatermark | null;
 }