T15-T18, T20, T23: app shell, three screens, and the first UI tests

Theme, go_router shell, record screen, trips list with selection, trip detail
with stats and charts, rename/delete/merge. 15 widget tests -- the first this
project has ever had, closing the gap docs/v3/BACKLOG.md names as v2's largest.

The theme sets bodyColor and displayColor explicitly rather than relying on a
wrapping widget, so the black-on-black regression cannot recur by someone
removing a container, and a widget test now asserts the headline names a colour
distinct from the ground.

Those tests immediately found a real layout bug: with a ride active the record
screen grows to six stat rows and overflows a short screen. Compose clipped this
silently, so it may be latent in the native app; Flutter reports it. Fixed by
making the screen scrollable while still centring when there is room.

Two harness lessons. pumpAndSettle never settles against a repeating timer, so
the elapsed clock now runs only while a ride is active -- better behaviour
anyway, since an idle screen has no clock to advance. And flutter_test asserts
no Timer is pending after disposal, which Drift's stream-query keep-alive cache
trips; tests now tear the tree down and pump past that window.

160 tests passing, analyze clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/src/ui/components/stats.dart

@@ -0,0 +1,155 @@
+/// Shared display components.
+///
+/// Ported from `com.rippr.ui.components.Stats`.
+library;
+
+import 'package:flutter/material.dart';
+
+import '../theme.dart';
+
+/// The one number that matters, rendered large.
+///
+/// Keyed so widget tests can find a specific readout by name rather than by matching
+/// text that may legitimately appear twice on screen.
+class BigStat extends StatelessWidget {
+  const BigStat({
+    super.key,
+    required this.label,
+    required this.value,
+    required this.unit,
+  });
+
+  final String label;
+  final String value;
+  final String unit;
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = Theme.of(context).colorScheme;
+    return Column(
+      crossAxisAlignment: CrossAxisAlignment.center,
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        Text(
+          label,
+          style: TextStyle(
+            fontSize: 13,
+            letterSpacing: 2,
+            color: colors.outline,
+          ),
+        ),
+        Row(
+          mainAxisAlignment: MainAxisAlignment.center,
+          crossAxisAlignment: CrossAxisAlignment.baseline,
+          textBaseline: TextBaseline.alphabetic,
+          children: [
+            Text(
+              value,
+              style: monoDigits.copyWith(
+                fontSize: 64,
+                fontWeight: FontWeight.bold,
+                // Named explicitly. The Compose version rendered black-on-black when the
+                // ambient content colour went missing.
+                color: colors.onSurface,
+              ),
+            ),
+            Text(
+              ' $unit',
+              style: TextStyle(fontSize: 18, color: colors.outline),
+            ),
+          ],
+        ),
+      ],
+    );
+  }
+}
+
+class StatRow extends StatelessWidget {
+  const StatRow({super.key, required this.label, required this.value});
+
+  final String label;
+  final String value;
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = Theme.of(context).colorScheme;
+    return Padding(
+      padding: const EdgeInsets.symmetric(vertical: 4),
+      child: Row(
+        mainAxisAlignment: MainAxisAlignment.spaceBetween,
+        children: [
+          Text(label, style: TextStyle(color: colors.outline)),
+          Text(
+            value,
+            style: monoDigits.copyWith(
+              fontWeight: FontWeight.w500,
+              color: colors.onSurface,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+/// Confirmation for anything destructive. Returns true only if confirmed.
+Future<bool> confirmDialog(
+  BuildContext context, {
+  required String title,
+  required String message,
+  required String confirmLabel,
+}) async {
+  final result = await showDialog<bool>(
+    context: context,
+    builder: (context) => AlertDialog(
+      title: Text(title),
+      content: Text(message),
+      actions: [
+        TextButton(
+          onPressed: () => Navigator.of(context).pop(false),
+          child: const Text('Cancel'),
+        ),
+        TextButton(
+          onPressed: () => Navigator.of(context).pop(true),
+          child: Text(
+            confirmLabel,
+            style: TextStyle(color: Theme.of(context).colorScheme.error),
+          ),
+        ),
+      ],
+    ),
+  );
+  return result ?? false;
+}
+
+/// A ride's worth of nothing. Used by the trips list and the detail charts.
+class EmptyState extends StatelessWidget {
+  const EmptyState({super.key, required this.message, this.icon});
+
+  final String message;
+  final IconData? icon;
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = Theme.of(context).colorScheme;
+    return Center(
+      child: Padding(
+        padding: const EdgeInsets.all(32),
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            if (icon != null) ...[
+              Icon(icon, size: 48, color: colors.outline),
+              const SizedBox(height: 16),
+            ],
+            Text(
+              message,
+              textAlign: TextAlign.center,
+              style: TextStyle(color: colors.outline),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}