Add groups with shared goals, objectives and chat; drop the water tracker

Groups let people keep each other honest: create one or join with a
six-letter invite code. Each group has shared goals split into measurable
objectives (km, sessions, words) that every member logs toward, a
leaderboard of kept rate and streak with nudges, and a group chat where
check-ins and nudges appear as cards beside the talk. The open chat polls
for new messages.

Reached from a new Groups tab (Training moves into the day rail), a Home
"Your groups" rail that opens the chat, and a Group tile in the add sheet.
Mock mode seeds two groups, a joinable one and members who reply.

The water tracker is removed; it did not fit the app. Bottom sheets are
now square app-wide via the theme.

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

frontend/lib/Grounded/comms/Comms.dart

@@ -9,6 +9,12 @@ import '../about/external/initial/CompletionRequest.dart';
 import '../about/external/initial/DeferralRequest.dart';
 import '../about/external/initial/DeviceRequest.dart';
 import '../about/external/initial/GoalRequest.dart';
+import '../about/external/initial/GroupGoalRequest.dart';
+import '../about/external/initial/GroupMessageRequest.dart';
+import '../about/external/initial/GroupRequest.dart';
+import '../about/external/initial/JoinGroupRequest.dart';
+import '../about/external/initial/NudgeRequest.dart';
+import '../about/external/initial/ObjectiveProgressRequest.dart';
 import '../about/external/initial/IdRequest.dart';
 import '../about/external/initial/LoginData.dart';
 import '../about/external/initial/ReportCardRequest.dart';
@@ -512,4 +518,76 @@ class Comms implements ConnectComms {
     dio.options.headers = navigation.value;
     return await dio.post(navigation.key, data: request);
   }
+
+  // ── Groups ────────────────────────────────────────────────────────────────
+
+  @override
+  Future<Response> getMyGroups(HistoryRequest request) async {
+    Pair navigation = await getRequestHeaders(myGroups, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> getGroupEntry(IdRequest request) async {
+    Pair navigation = await getRequestHeaders(oneGroup, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> saveGroupEntry(GroupRequest request) async {
+    Pair navigation = await getRequestHeaders(saveGroup, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> joinGroupEntry(JoinGroupRequest request) async {
+    Pair navigation = await getRequestHeaders(joinGroup, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> leaveGroupEntry(IdRequest request) async {
+    Pair navigation = await getRequestHeaders(leaveGroup, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> saveGroupGoalEntry(GroupGoalRequest request) async {
+    Pair navigation = await getRequestHeaders(saveGroupGoal, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> logObjectiveProgress(ObjectiveProgressRequest request) async {
+    Pair navigation = await getRequestHeaders(logObjective, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> getGroupMessages(IdRequest request) async {
+    Pair navigation = await getRequestHeaders(groupMessages, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> sendGroupMessage(GroupMessageRequest request) async {
+    Pair navigation = await getRequestHeaders(sendGroupMessageTo, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
+
+  @override
+  Future<Response> nudgeGroupMember(NudgeRequest request) async {
+    Pair navigation = await getRequestHeaders(nudgeMember, "");
+    dio.options.headers = navigation.value;
+    return await dio.post(navigation.key, data: request);
+  }
 }