feat: tablet landscape improvements

Shell: move Projects/News/Calendar into ShellRoute so the NavigationRail
persists across all screens. Show all 6 nav destinations on tablet
instead of 3+More overflow. Phone bottom nav unchanged.

Chat: master-detail layout on tablet — conversations list (320px) with
inline chat panel. Tapping a conversation updates state instead of
pushing a new route.

Knowledge: responsive grid (2 cols portrait, 3 cols landscape) with
card layout showing icon, title, body preview, and tags. Fix snippet
data — read json['snippet'] which the API actually sends. Bump snippet
length from 120 to 200 chars. Tasks now show description as snippet.

News: responsive grid with the same breakpoints. Larger snippet
(5 lines) in grid mode via snippetMaxLines parameter.

Briefing: centered reading column (maxWidth 700) on wide screens,
matching the web UI layout.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/widgets/knowledge_item_card.dart

@@ -27,12 +27,24 @@ class KnowledgeItemCard extends StatelessWidget {
 
   String? get _subtitle {
     if (item.noteType == 'task') {
+      if (item.body.trim().isNotEmpty) {
+        final preview = item.body.trim().replaceAll('\n', ' ');
+        return preview.length > 200 ? '${preview.substring(0, 200)}…' : preview;
+      }
       if (item.dueDate != null) return 'Due ${item.dueDate}';
       return item.status;
     }
     if (item.body.trim().isEmpty) return null;
     final preview = item.body.trim().replaceAll('\n', ' ');
-    return preview.length > 120 ? '${preview.substring(0, 120)}…' : preview;
+    return preview.length > 200 ? '${preview.substring(0, 200)}…' : preview;
+  }
+
+  void _onTap(BuildContext context) {
+    if (item.noteType == 'task') {
+      context.push('/tasks/${item.id}/edit');
+    } else {
+      context.push('/notes/${item.id}');
+    }
   }
 
   @override
@@ -53,13 +65,64 @@ class KnowledgeItemCard extends StatelessWidget {
             )
           : null,
       trailing: item.tags.isNotEmpty ? _TagChips(tags: item.tags) : null,
-      onTap: () {
-        if (item.noteType == 'task') {
-          context.push('/tasks/${item.id}/edit');
-        } else {
-          context.push('/notes/${item.id}');
-        }
-      },
+      onTap: () => _onTap(context),
+    );
+  }
+
+  Widget buildGridCard(BuildContext context) {
+    final scheme = Theme.of(context).colorScheme;
+    final textTheme = Theme.of(context).textTheme;
+    return Card(
+      elevation: 0,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(10),
+        side: BorderSide(color: scheme.outlineVariant),
+      ),
+      child: InkWell(
+        borderRadius: BorderRadius.circular(10),
+        onTap: () => _onTap(context),
+        child: Padding(
+          padding: const EdgeInsets.all(12),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Row(
+                children: [
+                  Icon(_icon, size: 18, color: _statusColor(context)),
+                  const SizedBox(width: 8),
+                  Expanded(
+                    child: Text(
+                      item.title.isEmpty ? '(untitled)' : item.title,
+                      maxLines: 2,
+                      overflow: TextOverflow.ellipsis,
+                      style: textTheme.titleSmall
+                          ?.copyWith(fontWeight: FontWeight.w600),
+                    ),
+                  ),
+                ],
+              ),
+              if (_subtitle != null) ...[
+                const SizedBox(height: 8),
+                Expanded(
+                  child: Text(
+                    _subtitle!,
+                    overflow: TextOverflow.ellipsis,
+                    maxLines: 4,
+                    style: textTheme.bodySmall?.copyWith(
+                      color: scheme.onSurfaceVariant,
+                      height: 1.4,
+                    ),
+                  ),
+                ),
+              ],
+              if (item.tags.isNotEmpty) ...[
+                const Spacer(),
+                _TagChips(tags: item.tags),
+              ],
+            ],
+          ),
+        ),
+      ),
     );
   }
 }

lib/widgets/news_card.dart

@@ -54,6 +54,7 @@ class NewsCard extends StatelessWidget {
   final String? reaction; // 'up' | 'down' | null
   final void Function(int itemId, String reaction) onReaction;
   final VoidCallback? onDiscuss;
+  final int snippetMaxLines;
 
   const NewsCard({
     super.key,
@@ -61,6 +62,7 @@ class NewsCard extends StatelessWidget {
     required this.reaction,
     required this.onReaction,
     this.onDiscuss,
+    this.snippetMaxLines = 2,
   });
 
   Future<void> _openUrl() async {
@@ -135,7 +137,7 @@ class NewsCard extends StatelessWidget {
               const SizedBox(height: 4),
               Text(
                 item.snippet,
-                maxLines: 2,
+                maxLines: snippetMaxLines,
                 overflow: TextOverflow.ellipsis,
                 style: textTheme.bodySmall?.copyWith(
                   color: scheme.onSurfaceVariant,