fix(i18n): comprehensive translation audit and fixes across all 14 languages

- Fix critical bug: Photos and Files pages had German text hardcoded in JSX,
  now use t() keys visible correctly in all languages
- Add 16 new translation keys (photos/files UI, login validation, common errors,
  rate limit message) across all 14 language files
- Add missing keys in packing, memories, and budget sections for br, de, it, es,
  fr, nl, pl, cs, hu, ru, zh, zh-TW, ar
- Add 152+ missing keys for zh-TW (entire sections were absent)
- Change Vacay addon name to 'Férias' in pt-BR only
- Add client-side HTTP 429 interceptor that shows translated rate limit message
- Replace hardcoded English fallbacks in TripPlannerPage, DayPlanSidebar,
  DisplaySettingsTab, MapSettingsTab, AccountTab, and TodoListPanel with t()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/components/Photos/PhotoLightbox.tsx

@@ -149,7 +149,7 @@ export function PhotoLightbox({ photos, initialIndex, onClose, onUpdate, onDelet
                   value={caption}
                   onChange={e => setCaption(e.target.value)}
                   onKeyDown={e => e.key === 'Enter' && handleSaveCaption()}
-                  placeholder="Beschriftung hinzufügen..."
+                  placeholder={t('photos.addCaption')}
                   className="flex-1 bg-white/10 text-white border border-white/20 rounded-lg px-3 py-1.5 text-sm focus:outline-none focus:border-white/40"
                   autoFocus
                 />
@@ -173,7 +173,7 @@ export function PhotoLightbox({ photos, initialIndex, onClose, onUpdate, onDelet
                   className="text-white text-sm flex-1 cursor-pointer hover:text-white/80"
                   onClick={() => setEditCaption(true)}
                 >
-                  {photo.caption || <span className="text-white/40 italic">Beschriftung hinzufügen...</span>}
+                  {photo.caption || <span className="text-white/40 italic">{t('photos.addCaption')}</span>}
                 </p>
                 <button
                   onClick={() => setEditCaption(true)}

client/src/components/Photos/PhotoUpload.tsx

@@ -85,10 +85,10 @@ export function PhotoUpload({ tripId, days, places, onUpload, onClose }: PhotoUp
         <input {...getInputProps()} />
         <Upload className={`w-10 h-10 mx-auto mb-3 ${isDragActive ? 'text-slate-900' : 'text-gray-400'}`} />
         {isDragActive ? (
-          <p className="text-slate-700 font-medium">Fotos hier ablegen...</p>
+          <p className="text-slate-700 font-medium">{t('photos.dropHere')}</p>
         ) : (
           <>
-            <p className="text-gray-600 font-medium">Fotos hier ablegen</p>
+            <p className="text-gray-600 font-medium">{t('photos.dropHereActive')}</p>
             <p className="text-gray-400 text-sm mt-1">{t('photos.clickToSelect')}</p>
             <p className="text-gray-400 text-xs mt-2">JPG, PNG, WebP · max. 10 MB · bis zu 30 Fotos</p>
           </>
@@ -152,12 +152,12 @@ export function PhotoUpload({ tripId, days, places, onUpload, onClose }: PhotoUp
             </select>
           </div>
           <div className="col-span-2">
-            <label className="block text-xs font-medium text-gray-700 mb-1">Beschriftung (für alle)</label>
+            <label className="block text-xs font-medium text-gray-700 mb-1">{t('photos.captionForAll')}</label>
             <input
               type="text"
               value={caption}
               onChange={e => setCaption(e.target.value)}
-              placeholder="Optionale Beschriftung..."
+              placeholder={t('photos.captionPlaceholder')}
               className="w-full border border-gray-200 rounded-lg px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-slate-900"
             />
           </div>