feat(photos): justified (aspect-preserving) layout option

Adds a Grid/Justified toggle to the photos toolbar. Justified mode packs
tiles into Flickr-style rows scaled to the container width using each
photo's real aspect ratio (from the new /api/photos width/height, falling
back to 1:1 when missing). It composes with the virtualized renderer:
per-group materialization and the off-screen spacer height estimates are
both layout-aware. The choice persists in localStorage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JW6ghFMDtnRYuYNzZhb47M

static/css/views/photos.css

@@ -19,6 +19,7 @@
     display: flex;
     align-items: center;
     justify-content: flex-end;
+    gap: var(--space-3);
     padding: var(--space-2) var(--space-2) var(--space-1);
 }
 
@@ -54,6 +55,25 @@
     margin-bottom: var(--space-4);
 }
 
+/* Justified (aspect-preserving) layout — the grid becomes a column of rows;
+   tile sizes are set inline by photos.js (see _justifiedRows). */
+.photos-layout-justified .photos-grid {
+    display: flex;
+    flex-direction: column;
+    gap: var(--space-2);
+}
+
+.photos-jrow {
+    display: flex;
+    flex-direction: row;
+    gap: var(--space-2);
+}
+
+.photos-layout-justified .photo-tile {
+    aspect-ratio: auto;
+    flex: 0 0 auto;
+}
+
 /* Monthly mode — larger tiles, more breathing room */
 .photos-group-monthly .photos-grid {
     grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));