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/css/views/photosLightbox.css

@@ -0,0 +1,194 @@
+/* Photos lightbox overlay */
+.photos-lightbox {
+    position: fixed;
+    inset: 0;
+    z-index: 10000;
+    background: rgba(0, 0, 0, 0.92);
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    opacity: 0;
+    transition: opacity 0.2s ease;
+    pointer-events: none;
+}
+
+.photos-lightbox.active {
+    opacity: 1;
+    pointer-events: auto;
+}
+
+/* Main content area */
+.lightbox-content {
+    position: relative;
+    max-width: 90vw;
+    max-height: 85vh;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+}
+
+.lightbox-content img,
+.lightbox-content video {
+    max-width: 90vw;
+    max-height: 85vh;
+    object-fit: contain;
+    border-radius: 4px;
+    user-select: none;
+}
+
+/* Navigation arrows */
+.lightbox-nav {
+    position: absolute;
+    top: 50%;
+    transform: translateY(-50%);
+    width: 48px;
+    height: 48px;
+    border-radius: 50%;
+    border: none;
+    background: rgba(255, 255, 255, 0.12);
+    color: #fff;
+    font-size: 20px;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    transition: background 0.15s;
+    z-index: 10001;
+}
+
+.lightbox-nav:hover {
+    background: rgba(255, 255, 255, 0.25);
+}
+
+.lightbox-prev {
+    left: 20px;
+}
+
+.lightbox-next {
+    right: 20px;
+}
+
+/* Close button */
+.lightbox-close {
+    position: absolute;
+    top: 16px;
+    right: 16px;
+    width: 40px;
+    height: 40px;
+    border-radius: 50%;
+    border: none;
+    background: rgba(255, 255, 255, 0.12);
+    color: #fff;
+    font-size: 18px;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    transition: background 0.15s;
+    z-index: 10001;
+}
+
+.lightbox-close:hover {
+    background: rgba(255, 255, 255, 0.25);
+}
+
+/* Top info bar */
+.lightbox-info {
+    position: absolute;
+    top: 0;
+    left: 0;
+    right: 0;
+    padding: 16px 70px 16px 20px;
+    background: linear-gradient(to bottom, rgba(0,0,0,0.6), transparent);
+    color: #fff;
+    z-index: 10001;
+}
+
+.lightbox-filename {
+    font-size: 15px;
+    font-weight: 600;
+    margin-bottom: 2px;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+}
+
+.lightbox-meta {
+    font-size: 12px;
+    color: rgba(255, 255, 255, 0.7);
+    display: flex;
+    gap: 12px;
+    flex-wrap: wrap;
+}
+
+/* Bottom toolbar */
+.lightbox-toolbar {
+    position: absolute;
+    bottom: 0;
+    left: 0;
+    right: 0;
+    padding: 16px 20px;
+    background: linear-gradient(to top, rgba(0,0,0,0.6), transparent);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 8px;
+    z-index: 10001;
+}
+
+.lightbox-toolbar button {
+    background: rgba(255, 255, 255, 0.12);
+    border: none;
+    color: #fff;
+    width: 40px;
+    height: 40px;
+    border-radius: 50%;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    font-size: 16px;
+    transition: background 0.15s;
+}
+
+.lightbox-toolbar button:hover {
+    background: rgba(255, 255, 255, 0.25);
+}
+
+.lightbox-toolbar button.active {
+    color: #ff5e3a;
+}
+
+/* Counter */
+.lightbox-counter {
+    position: absolute;
+    bottom: 16px;
+    left: 20px;
+    color: rgba(255, 255, 255, 0.5);
+    font-size: 13px;
+    z-index: 10001;
+}
+
+/* Responsive */
+@media (max-width: 768px) {
+    .lightbox-nav {
+        width: 36px;
+        height: 36px;
+        font-size: 16px;
+    }
+
+    .lightbox-prev {
+        left: 8px;
+    }
+
+    .lightbox-next {
+        right: 8px;
+    }
+
+    .lightbox-content img,
+    .lightbox-content video {
+        max-width: 100vw;
+        max-height: 80vh;
+    }
+}