Add Coach, take the reference's colours and copy its nav and motion

Coach is the centre tab: questions about routines, slips, streak, today,
active time and debt, answered on the device from the user's own data,
with a target bar chart and buttons that start routines or open the right
screen. The palette moves to neutral grey, near-black and one orange
accent, and Home's header becomes a light panel. The nav is now
overlapping frosted circles whose active disc pops forward, and tabs fade
and rise in on switch. Goals leaves the nav for Coach and stays one tap
away in Home's category row.

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

frontend/lib/Grounded/about/internal/application/CoachMessage.dart

@@ -0,0 +1,28 @@
+import 'CoachAction.dart';
+import 'CoachChart.dart';
+
+/// One turn in the coach thread. Answers carry **bold** markup in [body] and
+/// [followUp], an optional chart between them, and actions under them.
+class CoachMessage {
+  bool mine;
+
+  String body;
+
+  CoachChart? chart;
+
+  String followUp;
+
+  List<CoachAction> actions;
+
+  DateTime at;
+
+  CoachMessage({
+    required this.mine,
+    required this.body,
+    this.chart,
+    this.followUp = "",
+    List<CoachAction>? actions,
+    DateTime? at,
+  })  : actions = actions ?? <CoachAction>[],
+        at = at ?? DateTime.now();
+}