V3-01: activity type per ride

Adds Activity (motorcycle/bicycle/scooter/skateboard/running/walking/other) as
a column on Trip, and threads it through as real behaviour rather than a label:
ActivityProfile (domain/activity_profile.dart) carries a noise floor, accuracy
gate, histogram bucket width, and elevation smoothing window/threshold per
activity, consumed by sanitizeSpeedKmh, isUsableFix, computeSummary, Accumulator
and speedHistogram. The motorcycle profile reproduces the exact constants the
app shipped with before this existed, and a test asserts they never drift apart.

This is the port's first real migration: schemaVersion 1 -> 2,
m.addColumn(trips, trips.activity) with a motorcycle default so every existing
row survives unmodified. Proven with a hand-built v1 SQLite file (raw sqlite3,
not drift_dev's schema tooling) that a real database with real rides upgrades
and keeps every trip, segment and point.

No picker in front of Start: a new trip defaults to whichever activity was most
recently used, derived live from the trips table rather than duplicated into a
Config field. Editable afterwards on trip detail, which recomputes aggregates
under the new profile immediately -- a walking pace that reads as noise under a
motorcycle's floor reads as real movement once the activity is corrected, and
there's a test proving exactly that transition.

The widget-test pass for the activity-picker sheet caught a real overflow bug:
seven options overflowed a Column-based bottom sheet the same way the record
screen once did. Fixed with a scrollable ListView + isScrollControlled, same
shape as that earlier fix.

188 tests (171 -> 188): 2 migration, 5 ActivityProfile, 3 profile-threading
proofs in computeSummary, 5 repository, 2 widget. Analyze clean.

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

lib/src/ui/detail/trip_detail_screen.dart

@@ -8,10 +8,12 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../../app/providers.dart';
-import '../../export/export_manager.dart';
+import '../../domain/activity_profile.dart';
 import '../../domain/models.dart';
+import '../../export/export_manager.dart';
 import '../../stats/ride_statistics.dart';
 import '../../telemetry/telemetry.dart';
+import '../activity_display.dart';
 import '../components/ride_map.dart';
 import '../components/stats.dart';
 import '../format.dart';
@@ -50,13 +52,17 @@ final tripDetailProvider = FutureProvider.autoDispose.family<TripDetail?, int>((
 
   final points = await repo.pointsForTrip(tripId);
   final segments = await repo.segmentsForTrip(tripId);
+  final activityProfile = ActivityProfile.forActivity(trip.activity);
 
   return TripDetail(
     trip: trip,
-    summary: computeSummary(points, segments: segments),
+    summary: computeSummary(points, segments: segments, profile: activityProfile),
     points: points,
     segments: segments,
-    histogram: speedHistogram(points),
+    histogram: speedHistogram(
+      points,
+      bucketKmh: activityProfile.histogramBucketKmh,
+    ),
     profile: elevationProfile(points),
     mapEnabled: ref.watch(mapEnabledProvider),
   );
@@ -101,7 +107,10 @@ class TripDetailScreen extends ConsumerWidget {
           message: 'This ride no longer exists.',
           icon: Icons.help_outline,
         ),
-        AsyncValue(hasValue: true, value: final d?) => _Body(detail: d),
+        AsyncValue(hasValue: true, value: final d?) => _Body(
+          detail: d,
+          onEditActivity: () => _editActivity(context, ref, d.trip),
+        ),
         AsyncValue(hasError: true, :final error) => EmptyState(
           message: 'Could not load this ride.\n$error',
         ),
@@ -174,12 +183,46 @@ class TripDetailScreen extends ConsumerWidget {
     await ref.read(tripRepositoryProvider).renameTrip(trip.id, name);
     ref.invalidate(tripDetailProvider(trip.id));
   }
+
+  /// No picker in front of Start — V3-01's constraint — but a ride's activity is fully
+  /// editable here after the fact, the same pattern as rename.
+  Future<void> _editActivity(BuildContext context, WidgetRef ref, Trip trip) async {
+    final chosen = await showModalBottomSheet<Activity>(
+      context: context,
+      // Seven options, unlike the two-item export sheet -- a plain Column with
+      // mainAxisSize.min overflowed on a short screen. Scrollable rather than fixed.
+      isScrollControlled: true,
+      builder: (context) => SafeArea(
+        child: ListView(
+          shrinkWrap: true,
+          children: [
+            for (final activity in Activity.values)
+              ListTile(
+                key: Key('activity-${activity.name}'),
+                leading: Icon(activityIcon(activity)),
+                title: Text(activityLabel(activity)),
+                trailing: activity == trip.activity
+                    ? const Icon(Icons.check)
+                    : null,
+                onTap: () => Navigator.of(context).pop(activity),
+              ),
+          ],
+        ),
+      ),
+    );
+    if (chosen == null || chosen == trip.activity) return;
+    // Recomputes aggregates under the new profile -- a noise floor tuned for a
+    // motorcycle should not silently keep governing a walk.
+    await ref.read(tripRepositoryProvider).setActivity(trip.id, chosen);
+    ref.invalidate(tripDetailProvider(trip.id));
+  }
 }
 
 class _Body extends StatelessWidget {
-  const _Body({required this.detail});
+  const _Body({required this.detail, required this.onEditActivity});
 
   final TripDetail detail;
+  final VoidCallback onEditActivity;
 
   @override
   Widget build(BuildContext context) {
@@ -195,6 +238,13 @@ class _Body extends StatelessWidget {
             unit: 'km',
           ),
         ),
+        const SizedBox(height: 16),
+        Center(
+          child: _ActivityRow(
+            activity: detail.trip.activity,
+            onTap: onEditActivity,
+          ),
+        ),
         const SizedBox(height: 24),
         if (detail.mapEnabled)
           RideMap(points: detail.points, segments: detail.segments),
@@ -246,6 +296,37 @@ class _Body extends StatelessWidget {
   }
 }
 
+/// A tappable "what this ride was" row — icon, label, and a small edit affordance.
+class _ActivityRow extends StatelessWidget {
+  const _ActivityRow({required this.activity, required this.onTap});
+
+  final Activity activity;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    final colors = Theme.of(context).colorScheme;
+    return InkWell(
+      key: const Key('activity-row'),
+      onTap: onTap,
+      borderRadius: BorderRadius.circular(8),
+      child: Padding(
+        padding: const EdgeInsets.symmetric(vertical: 6, horizontal: 8),
+        child: Row(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            Icon(activityIcon(activity), size: 16, color: colors.outline),
+            const SizedBox(width: 6),
+            Text(activityLabel(activity), style: TextStyle(color: colors.outline)),
+            const SizedBox(width: 4),
+            Icon(Icons.edit_outlined, size: 13, color: colors.outline),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
 class _SectionTitle extends StatelessWidget {
   const _SectionTitle(this.text);