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/js/app/navigation.js

@@ -73,7 +73,8 @@ const VIEW_FLAGS = {
     'shared': 'isSharedView',
     'recent': 'isRecentView',
     'favorites': 'isFavoritesView',
-    'trash': 'isTrashView'
+    'trash': 'isTrashView',
+    'photos': 'isPhotosView'
 };
 
 /**
@@ -114,6 +115,11 @@ function setCurrentSection(section) {
     if (section !== 'shared' && window.sharedView) {
         window.sharedView.hide();
     }
+
+    // Hide photosView when switching to any other section
+    if (section !== 'photos' && window.photosView) {
+        window.photosView.hide();
+    }
 }
 
 function switchToSharedView() {
@@ -223,7 +229,30 @@ function switchToRecentFilesView() {
     }
 }
 
+function switchToPhotosView() {
+    setCurrentSection('photos');
+
+    // Hide breadcrumb
+    const breadcrumb = document.querySelector('.breadcrumb');
+    if (breadcrumb) breadcrumb.style.display = 'none';
+
+    // Hide actions-bar (photos has its own upload via selection bar)
+    window.setActionsBarMode('hidden');
+
+    // Hide file containers
+    const filesGrid = document.getElementById('files-grid');
+    const filesListView = document.getElementById('files-list-view');
+    if (filesGrid) filesGrid.style.display = 'none';
+    if (filesListView) filesListView.style.display = 'none';
+
+    // Show photos view
+    if (window.photosView) {
+        window.photosView.show();
+    }
+}
+
 window.switchToFilesView = switchToFilesView;
 window.switchToSharedView = switchToSharedView;
 window.switchToFavoritesView = switchToFavoritesView;
 window.switchToRecentFilesView = switchToRecentFilesView;
+window.switchToPhotosView = switchToPhotosView;