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/data/database.dart

@@ -45,6 +45,11 @@ class Trips extends Table {
 
   TextColumn get state => textEnum<domain.TripState>()();
 
+  /// Defaults to motorcycle so existing rows survive the migration that adds this
+  /// column unchanged — see [MigrationStrategy.onUpgrade] below.
+  TextColumn get activity =>
+      textEnum<domain.Activity>().withDefault(const Constant('motorcycle'))();
+
   RealColumn get distanceM => real().withDefault(const Constant(0))();
   IntColumn get movingMillis => integer().withDefault(const Constant(0))();
   RealColumn get maxSpeedKmh => real().withDefault(const Constant(0))();
@@ -101,11 +106,18 @@ class AppDatabase extends _$AppDatabase {
   AppDatabase(super.e);
 
   @override
-  int get schemaVersion => 1;
+  int get schemaVersion => 2;
 
   @override
   MigrationStrategy get migration => MigrationStrategy(
     onCreate: (m) => m.createAll(),
+    // The port's first real migration. The destructive fallback the native app removed
+    // in v2 stays removed here too — see the file doc comment above.
+    onUpgrade: (m, from, to) async {
+      if (from < 2) {
+        await m.addColumn(trips, trips.activity);
+      }
+    },
     beforeOpen: (details) async {
       // Non-negotiable: without this the CASCADE relationships above do nothing.
       await customStatement('PRAGMA foreign_keys = ON');
@@ -165,6 +177,7 @@ class AppDatabase extends _$AppDatabase {
       endedAt: Value(trip.endedAt),
       name: Value(trip.name),
       state: trip.state,
+      activity: Value(trip.activity),
       distanceM: Value(trip.distanceM),
       movingMillis: Value(trip.movingMillis),
       maxSpeedKmh: Value(trip.maxSpeedKmh),
@@ -173,6 +186,23 @@ class AppDatabase extends _$AppDatabase {
     ),
   );
 
+  Future<void> setTripActivity(int id, domain.Activity activity) => (update(
+    trips,
+  )..where((t) => t.id.equals(id))).write(
+    TripsCompanion(activity: Value(activity)),
+  );
+
+  /// The most recently created trip, regardless of state — used to default a new ride's
+  /// activity to whatever was last used, so there is no picker in front of Start.
+  Future<domain.Trip?> mostRecentTrip() async {
+    final row =
+        await (select(trips)
+              ..orderBy([(t) => OrderingTerm.desc(t.id)])
+              ..limit(1))
+            .getSingleOrNull();
+    return row == null ? null : _toTrip(row);
+  }
+
   Future<void> renameTrip(int id, String? name) => (update(
     trips,
   )..where((t) => t.id.equals(id))).write(TripsCompanion(name: Value(name)));
@@ -420,6 +450,7 @@ domain.Trip _toTrip(TripRow r) => domain.Trip(
   endedAt: r.endedAt,
   name: r.name,
   state: r.state,
+  activity: r.activity,
   distanceM: r.distanceM,
   movingMillis: r.movingMillis,
   maxSpeedKmh: r.maxSpeedKmh,