feat(photos): add Photos timeline view with lightbox and infinite scroll

Backend: new GET /api/photos endpoint with cursor-based pagination that
queries image/video files sorted by EXIF captured_at (falling back to
created_at), joining file_metadata for sort dates.

Frontend: dense photo grid grouped by day with lazy-loaded thumbnails,
IntersectionObserver infinite scroll, multi-select with batch
download/delete, and a full-screen lightbox with prev/next navigation,
EXIF metadata display, and download/favorite/delete toolbar.

Includes navigation wiring, CSS (with dark theme), and i18n translations
for all 9 locales.

static/locales/de.json

@@ -8,8 +8,14 @@
     "shared": "Geteilt",
     "recent": "Zuletzt verwendet",
     "favorites": "Favoriten",
+    "photos": "Fotos",
     "trash": "Papierkorb"
   },
+  "photos": {
+    "empty_state": "Noch keine Fotos",
+    "empty_hint": "Laden Sie Bilder oder Videos hoch, um sie hier zu sehen",
+    "items_selected": "ausgewählt"
+  },
   "actions": {
     "search": "Dateien suchen...",
     "new_folder": "Neuer Ordner",

static/locales/en.json

@@ -8,8 +8,14 @@
     "shared": "Shared",
     "recent": "Recent",
     "favorites": "Favorites",
+    "photos": "Photos",
     "trash": "Trash"
   },
+  "photos": {
+    "empty_state": "No photos yet",
+    "empty_hint": "Upload images or videos to see them here",
+    "items_selected": "selected"
+  },
   "actions": {
     "search": "Search files...",
     "new_folder": "New folder",

static/locales/es.json

@@ -8,8 +8,14 @@
     "shared": "Compartidos",
     "recent": "Recientes",
     "favorites": "Favoritos",
+    "photos": "Fotos",
     "trash": "Papelera"
   },
+  "photos": {
+    "empty_state": "Aún no hay fotos",
+    "empty_hint": "Sube imágenes o videos para verlos aquí",
+    "items_selected": "seleccionados"
+  },
   "share": {
     "dialogTitle": "Compartir Enlace",
     "linkLabel": "Enlace compartido:",

static/locales/fa.json

@@ -8,8 +8,14 @@
     "shared": "هم‌رسانی شده",
     "recent": "اخیر",
     "favorites": "موردعلاقه‌ها",
+    "photos": "عکس‌ها",
     "trash": "سطل زباله"
   },
+  "photos": {
+    "empty_state": "هنوز عکسی نیست",
+    "empty_hint": "تصاویر یا ویدیوها را آپلود کنید تا اینجا نمایش داده شوند",
+    "items_selected": "انتخاب شده"
+  },
   "actions": {
     "search": "جست‌و‌جوی پرونده‌ها..",
     "new_folder": "پوشهٔ جدید",

static/locales/fr.json

@@ -8,8 +8,14 @@
     "shared": "Partagés",
     "recent": "Récents",
     "favorites": "Favoris",
+    "photos": "Photos",
     "trash": "Corbeille"
   },
+  "photos": {
+    "empty_state": "Pas encore de photos",
+    "empty_hint": "Téléchargez des images ou des vidéos pour les voir ici",
+    "items_selected": "sélectionnés"
+  },
   "actions": {
     "search": "Rechercher des fichiers...",
     "new_folder": "Nouveau dossier",

static/locales/it.json

@@ -8,8 +8,14 @@
  "shared": "Condivisi",
  "recent": "Recenti",
  "favorites": "Preferiti",
+ "photos": "Foto",
  "trash": "Cestino"
  },
+ "photos": {
+   "empty_state": "Nessuna foto ancora",
+   "empty_hint": "Carica immagini o video per vederli qui",
+   "items_selected": "selezionati"
+ },
  "actions": {
  "search": "Cerca file...",
  "new_folder": "Nuova cartella",

static/locales/nl.json

@@ -8,8 +8,14 @@
     "shared": "Gedeeld",
     "recent": "Recente",
     "favorites": "Favorieten",
+    "photos": "Foto's",
     "trash": "Prullenbak"
   },
+  "photos": {
+    "empty_state": "Nog geen foto's",
+    "empty_hint": "Upload afbeeldingen of video's om ze hier te zien",
+    "items_selected": "geselecteerd"
+  },
   "actions": {
     "search": "Zoek bestanden...",
     "new_folder": "Nieuwe map",

static/locales/pt.json

@@ -8,8 +8,14 @@
     "shared": "Compartilhados",
     "recent": "Recentes",
     "favorites": "Favoritos",
+    "photos": "Fotos",
     "trash": "Lixeira"
   },
+  "photos": {
+    "empty_state": "Nenhuma foto ainda",
+    "empty_hint": "Envie imagens ou vídeos para vê-los aqui",
+    "items_selected": "selecionados"
+  },
   "actions": {
     "search": "Pesquisar arquivos...",
     "new_folder": "Nova pasta",

static/locales/zh.json

@@ -8,8 +8,14 @@
     "shared": "共享",
     "recent": "最近",
     "favorites": "收藏",
+    "photos": "照片",
     "trash": "回收站"
   },
+  "photos": {
+    "empty_state": "还没有照片",
+    "empty_hint": "上传图片或视频即可在此查看",
+    "items_selected": "已选择"
+  },
   "actions": {
     "search": "搜索文件...",
     "new_folder": "新建文件夹",