Show real photos for people instead of scene art

Your avatar is your photo, picked from the device by tapping it on Home or
from a new Profile photo row in Settings, shrunk to 256 px and kept on the
phone (there is no upload endpoint yet). Group members show the photo the
server sends in a new `photo` field, everywhere avatars appear. Without a
photo, an initial on a neutral disc. Mock mode bundles free Unsplash
portraits for the sample people.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KhQh614DMeYoQEH9SoMRUw

frontend/lib/Grounded/designs/Checkbox.dart

@@ -137,7 +137,8 @@ class TickRow extends StatelessWidget {
                       duration: const Duration(milliseconds: 160),
                       style: TextStyle(
                         fontSize: 15,
-                        fontFamily: struck ? "GroundedRegular" : "GroundedMedium",
+                        fontFamily:
+                            struck ? "GroundedRegular" : "GroundedMedium",
                         color: struck ? colorGrey2 : colorPrimaryDark,
                         decoration: struck
                             ? TextDecoration.lineThrough