feat(offline): tier 2 phase 4 — per-row pending-sync indicators

A small cloud-upload glyph appears next to any row whose id has a
queued offline write (offline-created temp ids and pending edits both
count). Tooltip reads "Pending sync — will save when online". Renders
nothing during normal online operation so the list stays clean.

- DB: `watchPendingIds(domain)` streams the union of target_id and
  temp_id across the queue, scoped per domain.
- Per-domain Riverpod stream providers for notes / tasks / projects.
- New `PendingSyncBadge` widget — used by KnowledgeItemCard (both
  list and grid variants), `_ProjectCard`, and `_TaskRow` in the
  project workspace.

flutter analyze clean; 21 tests pass. Closes #147 — all four phases
of Tier 2 offline mode are in place.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/widgets/pending_sync_badge.dart

@@ -0,0 +1,48 @@
+import 'package:flutter/material.dart';
+import 'package:lucide_icons/lucide_icons.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../data/local/database.dart';
+import '../providers/api_client_provider.dart';
+
+/// Small cloud-upload glyph shown next to a row whose id has a queued
+/// offline write (Phase 4). Renders nothing when the queue is empty for
+/// that id, so list views stay clean during normal online operation.
+class PendingSyncBadge extends ConsumerWidget {
+  final String domain;
+  final int id;
+  final double size;
+
+  const PendingSyncBadge({
+    super.key,
+    required this.domain,
+    required this.id,
+    this.size = 14,
+  });
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final pending = switch (domain) {
+      kSyncDomainNotes => ref.watch(pendingNoteIdsProvider).asData?.value,
+      kSyncDomainTasks => ref.watch(pendingTaskIdsProvider).asData?.value,
+      kSyncDomainProjects =>
+        ref.watch(pendingProjectIdsProvider).asData?.value,
+      _ => null,
+    };
+    if (pending == null || !pending.contains(id)) {
+      return const SizedBox.shrink();
+    }
+    final scheme = Theme.of(context).colorScheme;
+    return Tooltip(
+      message: 'Pending sync — will save when online',
+      child: Padding(
+        padding: const EdgeInsets.symmetric(horizontal: 4),
+        child: Icon(
+          LucideIcons.uploadCloud,
+          size: size,
+          color: scheme.onSurfaceVariant,
+        ),
+      ),
+    );
+  }
+}