Switch to Inter, round the corners softly and make the nav switch tabs

Inter replaces General Sans (Inter Display for titles and big numbers).
Corners come back from before the squaring commit, scaled to a soft set
(16 cards, 14 buttons, 12 rows, 8 chips) and applied to the screens built
since. The nav is now a cluster of round frosted buttons that switches
Today, Routines, Goals, Groups and Progress in place inside Home: no
pushed pages, no back arrows, and Android back returns to Today.

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

frontend/lib/Grounded/see/goal/GoalDetailState.dart

@@ -242,7 +242,7 @@ class GoalDetailState extends State<GoalDetail>
       padding: const EdgeInsets.fromLTRB(16, 14, 16, 14),
       decoration: BoxDecoration(
         color: colorWhite.withValues(alpha: 0.08),
-        borderRadius: BorderRadius.zero,
+        borderRadius: BorderRadius.circular(12),
       ),
       child: Column(
         mainAxisSize: MainAxisSize.min,
@@ -405,7 +405,7 @@ class GoalDetailState extends State<GoalDetail>
               width: 58,
               height: 58,
               child: ClipRRect(
-                borderRadius: BorderRadius.zero,
+                borderRadius: BorderRadius.circular(12),
                 child: SceneArt(
                   palette: scenePalette(routine.kind),
                   seed: sceneSeed(routine.title),
@@ -454,6 +454,7 @@ class GoalDetailState extends State<GoalDetail>
                   color: routine.kind == RoutineKind.MustDo
                       ? colorPrimaryDark
                       : tone,
+                  shape: BoxShape.circle,
                 ),
                 child: Icon(CupertinoIcons.play_fill,
                     size: 15, color: colorWhite),

frontend/lib/Grounded/see/goal/GoalEditorState.dart

@@ -282,7 +282,7 @@ class GoalEditorState extends State<GoalEditor> implements ConnectGoalEditor {
     return Container(
       padding: const EdgeInsets.all(18),
       decoration: BoxDecoration(
-        borderRadius: BorderRadius.zero,
+        borderRadius: BorderRadius.circular(14),
         gradient: LinearGradient(
           begin: Alignment.topLeft,
           end: Alignment.bottomRight,
@@ -338,6 +338,7 @@ class GoalEditorState extends State<GoalEditor> implements ConnectGoalEditor {
             alignment: Alignment.center,
             decoration: BoxDecoration(
               color: colour,
+              shape: BoxShape.circle,
               border: Border.all(
                 color: selected ? colorWhite : Colors.transparent,
                 width: 3,

frontend/lib/Grounded/see/goal/Goals.dart

@@ -3,7 +3,11 @@ import 'package:flutter/material.dart';
 import 'GoalsState.dart';
 
 class Goals extends StatefulWidget {
-  const Goals({super.key});
+  /// Shown as a tab inside Home: no back arrow, and room at the bottom
+  /// for the nav.
+  final bool tab;
+
+  const Goals({super.key, this.tab = false});
 
   @override
   State<Goals> createState() => GoalsState();

frontend/lib/Grounded/see/goal/GoalsState.dart

@@ -74,7 +74,8 @@ class GoalsState extends State<Goals> implements ConnectGoals {
     return Sheet(
       eyebrow: "Grounded",
       title: "Goals",
-      onBack: _onBack,
+      onBack: widget.tab ? null : _onBack,
+      bottomSpace: widget.tab ? 130 : 40,
       action: chromeAction(CupertinoIcons.add, _onNewGoal),
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,
@@ -120,7 +121,7 @@ class GoalsState extends State<Goals> implements ConnectGoals {
         height: 260,
         margin: const EdgeInsets.only(bottom: 14),
         decoration: BoxDecoration(
-          borderRadius: BorderRadius.zero,
+          borderRadius: BorderRadius.circular(16),
           boxShadow: const [
             BoxShadow(
               color: Color(0x262A3A30),
@@ -130,7 +131,7 @@ class GoalsState extends State<Goals> implements ConnectGoals {
           ],
         ),
         child: ClipRRect(
-          borderRadius: BorderRadius.zero,
+          borderRadius: BorderRadius.circular(16),
           child: Stack(
             fit: StackFit.expand,
             children: [
@@ -151,7 +152,7 @@ class GoalsState extends State<Goals> implements ConnectGoals {
                       children: [
                         GlassSurface(
                           onDark: true,
-                          radius: BorderRadius.zero,
+                          radius: BorderRadius.circular(14),
                           padding: const EdgeInsets.symmetric(
                               horizontal: 10, vertical: 5),
                           child: text(