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/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,