refactor: remove briefing digest card, show full message list directly

The summary card duplicated the first assistant message and consumed
screen real estate without benefit on small screens. Replaced with:
- Full message list via ChatMessageBubble from the top
- SliverFillRemaining empty state ("No briefing yet today" + generate button)
  when no messages exist

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

lib/screens/briefing/briefing_screen.dart

@@ -2,9 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../../core/exceptions.dart';
-import '../../data/models/message.dart';
 import '../../providers/briefing_provider.dart';
-import '../../widgets/briefing_digest_card.dart';
 import '../../widgets/chat_message_bubble.dart';
 import 'briefing_history_screen.dart';
 
@@ -146,59 +144,44 @@ class _BriefingScreenState extends ConsumerState<BriefingScreen> {
           ),
         ),
         data: (conv) {
-          // First assistant message for the digest card (null if none yet)
-          final Message? firstAssistant = conv.messages
-              .where((m) => m.role == MessageRole.assistant)
-              .toList()
-              .firstOrNull;
-
           return Column(
             children: [
-              // Digest card + messages share one scroll view so expanding the
-              // card doesn't trap the user — the whole page just becomes taller.
               Expanded(
                 child: CustomScrollView(
                   controller: _scrollController,
                   slivers: [
-                    SliverToBoxAdapter(
+                    if (conv.messages.isEmpty)
-                      child: BriefingDigestCard(
+                      SliverFillRemaining(
-                        message: firstAssistant,
+                        child: Center(
-                        onGenerateNow: _refresh,
+                          child: Column(
-                      ),
+                            mainAxisSize: MainAxisSize.min,
-                    ),
+                            children: [
-
+                              Text(
-                    if (conv.messages.isNotEmpty)
+                                'No briefing yet today.',
-                      SliverToBoxAdapter(
-                        child: Padding(
-                          padding: const EdgeInsets.symmetric(vertical: 4),
-                          child: Row(children: [
-                            const Expanded(child: Divider()),
-                            Padding(
-                              padding:
-                                  const EdgeInsets.symmetric(horizontal: 10),
-                              child: Text(
-                                'Conversation',
                                 style: Theme.of(context)
                                     .textTheme
-                                    .labelSmall
+                                    .bodyMedium
-                                    ?.copyWith(
+                                    ?.copyWith(color: scheme.onSurfaceVariant),
-                                        color: scheme.onSurfaceVariant),
                               ),
-                            ),
+                              const SizedBox(height: 12),
-                            const Expanded(child: Divider()),
+                              FilledButton.tonal(
-                          ]),
+                                onPressed: _refresh,
+                                child: const Text('Generate now'),
+                              ),
+                            ],
+                          ),
+                        ),
+                      )
+                    else
+                      SliverPadding(
+                        padding: const EdgeInsets.symmetric(
+                            horizontal: 8, vertical: 8),
+                        sliver: SliverList.builder(
+                          itemCount: conv.messages.length,
+                          itemBuilder: (_, i) =>
+                              ChatMessageBubble(message: conv.messages[i]),
                         ),
                       ),
-
-                    SliverPadding(
-                      padding: const EdgeInsets.symmetric(
-                          horizontal: 8, vertical: 8),
-                      sliver: SliverList.builder(
-                        itemCount: conv.messages.length,
-                        itemBuilder: (_, i) =>
-                            ChatMessageBubble(message: conv.messages[i]),
-                      ),
-                    ),
                   ],
                 ),
               ),