Move Order and Display mode to the Photos tab

Both are photos-specific settings (rotation order, how a photo's aspect
ratio gets reconciled with the panel), not device-wide configuration --
they belonged on the Photos tab next to the album/queue settings, not
Configuration. No backend change: both already save through the shared
partial-update /config endpoint regardless of which tab's form sends
them.

server/app/templates/frame_photos.html

@@ -30,6 +30,27 @@
               {% endfor %}
             </select>
           </label>
+          <label>Order
+            <select id="order">
+              <option value="sequential" {% if frame.order == "sequential" %}selected{% endif %}>Sequential</option>
+              <option value="shuffle" {% if frame.order == "shuffle" %}selected{% endif %}>Shuffle</option>
+            </select>
+          </label>
+          <label>Display mode
+            <select id="display_mode">
+              {% for mode, label in display_mode_labels.items() %}
+                <option value="{{ mode }}" {% if frame.display_mode == mode %}selected{% endif %}>{{ label }}</option>
+              {% endfor %}
+            </select>
+          </label>
+          <p class="sub" style="margin-top: 8px;">How a photo's aspect ratio
+            is reconciled with the panel's: <strong>Crop to fill</strong>
+            trims the excess; <strong>Crop to faces</strong> does the same
+            but shifts the crop to keep people on screen; <strong>Stretch to
+            fill</strong> fills the panel exactly without cropping (photos
+            not matching the panel's aspect ratio look stretched);
+            <strong>Shrink to fit</strong> shows the whole photo, letterboxed
+            if needed.</p>
           <button type="button" class="secondary" id="load-albums">Load Albums</button>
           <button type="submit">Save</button>
         </form>