diag(flutter): trace playlist provider — wire vs drift vs filter

Web UI shows system playlists; Flutter shows placeholders. Wire shape,
adapters, drift schema, and filter constants all line up on inspection,
so adding instrumentation to pinpoint where the system rows fall out:

- Log what /api/playlists?kind=all actually returns (owned/public
  counts, including how many of owned are system).
- Log what cacheFirst sees on each drift emit: total rows, filtered,
  how many are system, how many landed in owned vs pub, plus the
  user.id used for the owned-vs-pub split.

Also add the 3s connectivity timeout that albumProvider/artistProvider
got — keeps the alwaysRefresh path from blocking on a stalled
connectivity stream.

Three log lines from one home-screen visit will tell us:
- Does the server emit system rows? (wire log: system=N)
- Do they land in drift? (drift log: filtered system=N)
- Do they survive the user-id filter? (drift log: owned system=N)

flutter_client/lib/playlists/playlists_provider.dart

@@ -1,4 +1,5 @@
 import 'package:drift/drift.dart' as drift;
+import 'package:flutter/foundation.dart' show debugPrint;
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../api/endpoints/me.dart';
@@ -36,6 +37,11 @@ final playlistsListProvider =
     fetchAndPopulate: () async {
       final api = await ref.read(playlistsApiProvider.future);
       final fresh = await api.list(kind: kind);
+      final ownedSysCount =
+          fresh.owned.where((p) => p.systemVariant != null).length;
+      debugPrint(
+          'playlistsListProvider($kind): wire returned owned=${fresh.owned.length} '
+          '(system=$ownedSysCount) public=${fresh.public.length}');
       await db.batch((b) {
         for (final p in fresh.all) {
           b.insert(db.cachedPlaylists, p.toDrift(),
@@ -49,7 +55,7 @@ final playlistsListProvider =
         if (kind == 'user') return r.systemVariant == null;
         if (kind == 'system') return r.systemVariant != null;
         return true; // 'all'
-      });
+      }).toList();
       final owned = filtered
           .where((r) => r.userId == user.id)
           .map((r) => r.toRef())
@@ -58,9 +64,18 @@ final playlistsListProvider =
           .where((r) => r.userId != user.id && r.isPublic)
           .map((r) => r.toRef())
           .toList();
+      final ownedSys = owned.where((p) => p.isSystem).length;
+      final driftSys = filtered.where((r) => r.systemVariant != null).length;
+      debugPrint(
+          'playlistsListProvider($kind): drift rows=${rows.length} '
+          'filtered=${filtered.length} (system=$driftSys) '
+          'owned=${owned.length} (system=$ownedSys) pub=${pub.length} '
+          'userId=${user.id}');
       return PlaylistsList(owned: owned, public: pub);
     },
-    isOnline: () async => (await ref.read(connectivityProvider.future)),
+    isOnline: () async => (await ref
+        .read(connectivityProvider.future)
+        .timeout(const Duration(seconds: 3), onTimeout: () => true)),
     // Aggregate list — server may add system playlists (For-You /
     // Discover) that the per-user delta sync doesn't always emit.
     // Stale-while-revalidate ensures the home tile row reflects the