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/screens/knowledge/knowledge_screen.dart

@@ -186,18 +186,57 @@ class _KnowledgeScreenState extends ConsumerState<KnowledgeScreen>
     }
     return RefreshIndicator(
       onRefresh: () => ref.read(knowledgeProvider.notifier).refresh(),
-      child: ListView.separated(
-        controller: _scrollController,
-        itemCount: items.length + (state.isLoadingBatch ? 1 : 0),
-        separatorBuilder: (_, _) => const Divider(height: 1),
-        itemBuilder: (_, i) {
-          if (i >= items.length) {
-            return const Padding(
-              padding: EdgeInsets.all(16),
-              child: Center(child: CircularProgressIndicator()),
+      child: LayoutBuilder(
+        builder: (context, constraints) {
+          final cols = constraints.maxWidth >= 900
+              ? 3
+              : constraints.maxWidth >= 600
+                  ? 2
+                  : 1;
+          if (cols == 1) {
+            return ListView.separated(
+              controller: _scrollController,
+              itemCount: items.length + (state.isLoadingBatch ? 1 : 0),
+              separatorBuilder: (_, _) => const Divider(height: 1),
+              itemBuilder: (_, i) {
+                if (i >= items.length) {
+                  return const Padding(
+                    padding: EdgeInsets.all(16),
+                    child: Center(child: CircularProgressIndicator()),
+                  );
+                }
+                return KnowledgeItemCard(item: items[i]);
+              },
             );
           }
-          return KnowledgeItemCard(item: items[i]);
+          return CustomScrollView(
+            controller: _scrollController,
+            slivers: [
+              SliverPadding(
+                padding: const EdgeInsets.all(8),
+                sliver: SliverGrid(
+                  gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
+                    crossAxisCount: cols,
+                    crossAxisSpacing: 8,
+                    mainAxisSpacing: 8,
+                    childAspectRatio: 1.8,
+                  ),
+                  delegate: SliverChildBuilderDelegate(
+                    (_, i) {
+                      if (i >= items.length) {
+                        return const Center(
+                            child: CircularProgressIndicator());
+                      }
+                      return KnowledgeItemCard(item: items[i])
+                          .buildGridCard(context);
+                    },
+                    childCount:
+                        items.length + (state.isLoadingBatch ? 1 : 0),
+                  ),
+                ),
+              ),
+            ],
+          );
         },
       ),
     );