feat: photo/video capture-date pipeline + premium UI/UX overhaul

Backend — Photos timeline now groups by real capture date instead of upload time. New MediaMetadataService (FileLifecycleHook) extracts EXIF DateTimeOriginal from images and container creation_time from videos (mov/mp4/mkv) via nom-exif, timezone-correct (OffsetTimeOriginal), persisting captured_at so the existing media_sort_date trigger takes over. Adds POST /admin/photos/metadata/reextract to backfill existing media. Falls back to upload date when no embedded date exists.

Frontend — premium grid cards: combined metadata line (relative date · size, owner avatar when shared), custom selection checkbox with a clear checked state, uniform full-width 4:3 thumbnail tiles independent of filename length, centered file-type icons, and a hit-test fix so checkbox/star/kebab clicks reach the controls (the decorative thumbnail no longer captures pointer events). Notification messages internationalised across all 16 locales. Broader polish: design tokens, a11y/focus-visible states, brand + PWA assets.

Chore — bump semver-compatible dependencies (cargo upgrade); add nom-exif 3.6.1.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/interfaces/api/handlers/admin_handler.rs

@@ -58,6 +58,8 @@ pub fn admin_routes() -> Router<Arc<AppState>> {
         .route("/settings/registration", put(set_registration_setting))
         // Audio metadata
         .route("/audio/metadata/reextract", post(reextract_audio_metadata))
+        // Image/video capture metadata (Photos timeline backfill)
+        .route("/photos/metadata/reextract", post(reextract_image_metadata))
         // SMTP diagnostics
         .route("/smtp/info", get(get_smtp_info))
         .route("/smtp/test", post(send_smtp_test))
@@ -1216,6 +1218,32 @@ async fn reextract_audio_metadata(
     })))
 }
 
+/// Backfill image/video capture dates (EXIF / container creation time) into
+/// `storage.file_metadata` for every existing media file, re-bucketing the
+/// Photos timeline by real capture date. Safe to re-run (idempotent upsert).
+async fn reextract_image_metadata(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    admin_guard(&state, &headers).await?;
+
+    let result = state
+        .applications
+        .media_metadata_service
+        .reextract_all_image_metadata()
+        .await
+        .map_err(|e| {
+            AppError::internal_error(format!("Failed to re-extract capture metadata: {}", e))
+        })?;
+
+    Ok(Json(serde_json::json!({
+        "message": "Image/video capture-metadata extraction complete",
+        "total": result.total,
+        "processed": result.processed,
+        "failed": result.failed,
+    })))
+}
+
 // ─────────────────────────────────────────────────────
 // SMTP diagnostics
 // ─────────────────────────────────────────────────────

src/interfaces/api/handlers/file_handler.rs

@@ -370,7 +370,10 @@ impl FileHandler {
         {
             return Response::builder()
                 .status(StatusCode::OK)
-                .header(header::CONTENT_TYPE, "image/jpeg")
+                .header(
+                    header::CONTENT_TYPE,
+                    crate::common::mime_detect::thumbnail_content_type(&data),
+                )
                 .header(header::CONTENT_LENGTH, data.len())
                 .header(header::CACHE_CONTROL, "public, max-age=31536000, immutable")
                 .header(header::ETAG, &etag)
@@ -420,7 +423,10 @@ impl FileHandler {
         {
             return Response::builder()
                 .status(StatusCode::OK)
-                .header(header::CONTENT_TYPE, "image/jpeg")
+                .header(
+                    header::CONTENT_TYPE,
+                    crate::common::mime_detect::thumbnail_content_type(&data),
+                )
                 .header(header::CONTENT_LENGTH, data.len())
                 .header(header::CACHE_CONTROL, "public, max-age=31536000, immutable")
                 .header(header::ETAG, &etag)
@@ -440,7 +446,10 @@ impl FileHandler {
         {
             Ok(data) => Response::builder()
                 .status(StatusCode::OK)
-                .header(header::CONTENT_TYPE, "image/jpeg")
+                .header(
+                    header::CONTENT_TYPE,
+                    crate::common::mime_detect::thumbnail_content_type(&data),
+                )
                 .header(header::CONTENT_LENGTH, data.len())
                 .header(header::CACHE_CONTROL, "public, max-age=31536000, immutable")
                 .header(header::ETAG, &etag)