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/theme.dart

@@ -0,0 +1,65 @@
+/// Ported from `com.rippr.ui.theme.RipprTheme`.
+///
+/// Dark-only by design. This is read at a glance in daylight with a visor down, and a
+/// light theme would be actively worse for that.
+library;
+
+import 'package:flutter/material.dart';
+
+// Matches the launcher icon: near-black tarmac with a safety-orange accent.
+const _accent = Color(0xFFFF5722);
+const _ground = Color(0xFF101418);
+const _surface = Color(0xFF181D23);
+const _ink = Color(0xFFF2F5F8);
+const _outline = Color(0xFF66727E);
+const _danger = Color(0xFFE53935);
+
+const ripprColors = ColorScheme.dark(
+  primary: _accent,
+  onPrimary: Color(0xFF100A06),
+  secondary: _outline,
+  surface: _surface,
+  onSurface: _ink,
+  surfaceContainerHighest: Color(0xFF212832),
+  onSurfaceVariant: _ink,
+  outline: _outline,
+  error: _danger,
+  onError: _ink,
+);
+
+/// The near-black ground the whole app sits on.
+const ripprBackground = _ground;
+
+ThemeData ripprTheme() {
+  final base = ThemeData(
+    colorScheme: ripprColors,
+    useMaterial3: true,
+    scaffoldBackgroundColor: _ground,
+  );
+
+  return base.copyWith(
+    // Compose's `Surface` was load-bearing, not decoration: it set `LocalContentColor`.
+    // Without it, any Text that did not name a colour fell back to black — invisible on
+    // this near-black ground, and **no test caught it; only a screenshot did**.
+    //
+    // Flutter's equivalent exposure is the default text colour. Setting it explicitly
+    // here, rather than relying on a wrapping widget, means the failure cannot recur by
+    // someone removing a container.
+    textTheme: base.textTheme.apply(bodyColor: _ink, displayColor: _ink),
+    appBarTheme: const AppBarTheme(
+      backgroundColor: _ground,
+      foregroundColor: _ink,
+      elevation: 0,
+    ),
+    dividerTheme: const DividerThemeData(color: Color(0xFF2A323C), space: 1),
+  );
+}
+
+/// Monospace for anything numeric.
+///
+/// Digits that change every second must not make the layout jitter, which proportional
+/// figures do. Used for every speed, distance and clock in the app.
+const TextStyle monoDigits = TextStyle(
+  fontFamily: 'monospace',
+  fontFeatures: [FontFeature.tabularFigures()],
+);