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/about/external/initial/ObjectiveProgressRequest.dart

@@ -0,0 +1,24 @@
+/// Logs an amount against one objective of a shared goal.
+class ObjectiveProgressRequest {
+  String groupId;
+
+  String goalId;
+
+  String objectiveId;
+
+  double amount;
+
+  String note;
+
+  ObjectiveProgressRequest({this.groupId = "", this.goalId = "", this.objectiveId = "", this.amount = 0, this.note = ""});
+
+  Map<String, dynamic> toJson() {
+    final Map<String, dynamic> data = <String, dynamic>{};
+    data['groupId'] = groupId;
+    data['goalId'] = goalId;
+    data['objectiveId'] = objectiveId;
+    data['amount'] = amount;
+    data['note'] = note;
+    return data;
+  }
+}