feat(#172): block/unblock in contacts, DM, and discovery menus

Completes the A5 entry points: contact long-press sheet, DM app-bar overflow, and
discovery item sheet each get a Block/Unblock toggle (by pubkey, reflecting current
state). Pairs with the channel 'Block sender' from 8a2e764.

Epic A #165 / A5 #172. Design: docs/architecture/block-contract-as-built.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/screens/chat_screen.dart

@@ -27,6 +27,7 @@ import '../models/app_settings.dart';
 import '../models/path_history.dart';
 import '../models/translation_support.dart';
 import '../services/app_settings_service.dart';
+import '../services/block_service.dart';
 import '../services/chat_text_scale_service.dart';
 import '../services/path_history_service.dart';
 import '../services/translation_service.dart';
@@ -353,8 +354,22 @@ class _ChatScreenState extends State<ChatScreen> {
                   if (value == 'clearChat') {
                     connector.clearMessagesForContact(widget.contact);
                   }
+                  if (value == 'block') {
+                    context.read<BlockService>().block(
+                      widget.contact.publicKeyHex,
+                    );
+                  }
+                  if (value == 'unblock') {
+                    context.read<BlockService>().unblock(
+                      widget.contact.publicKeyHex,
+                    );
+                  }
                 },
-                itemBuilder: (context) => [
+                itemBuilder: (context) {
+                  final isBlocked = context.read<BlockService>().isBlocked(
+                    widget.contact.publicKeyHex,
+                  );
+                  return [
                     PopupMenuItem(
                       value: 'info',
                       child: Row(
@@ -398,7 +413,28 @@ class _ChatScreenState extends State<ChatScreen> {
                         ],
                       ),
                     ),
+                    PopupMenuItem(
+                      value: isBlocked ? 'unblock' : 'block',
+                      child: Row(
+                        children: [
+                          Icon(
+                            isBlocked
+                                ? Icons.check_circle_outline
+                                : Icons.block,
+                            size: 20,
+                            color: isBlocked ? null : Colors.red.shade700,
+                          ),
+                          const SizedBox(width: 12),
+                          Text(
+                            isBlocked
+                                ? context.l10n.block_unblock
+                                : context.l10n.block_block,
+                          ),
                         ],
+                      ),
+                    ),
+                  ];
+                },
               );
             },
           ),

lib/screens/contacts_screen.dart

@@ -1259,6 +1259,8 @@ class _ContactsScreenState extends State<ContactsScreen>
     final isRepeater = contact.type == advTypeRepeater;
     final isRoom = contact.type == advTypeRoom;
     final isFavorite = contact.isFavorite;
+    final blockService = context.read<BlockService>();
+    final isBlocked = blockService.isBlocked(contact.publicKeyHex);
 
     showModalBottomSheet(
       context: context,
@@ -1266,6 +1268,25 @@ class _ContactsScreenState extends State<ContactsScreen>
         child: Column(
           mainAxisSize: MainAxisSize.min,
           children: [
+            ListTile(
+              leading: Icon(
+                isBlocked ? Icons.check_circle_outline : Icons.block,
+                color: isBlocked ? null : Colors.red.shade700,
+              ),
+              title: Text(
+                isBlocked
+                    ? context.l10n.block_unblock
+                    : context.l10n.block_block,
+              ),
+              onTap: () async {
+                Navigator.pop(sheetContext);
+                if (isBlocked) {
+                  await blockService.unblock(contact.publicKeyHex);
+                } else {
+                  await blockService.block(contact.publicKeyHex);
+                }
+              },
+            ),
             if (isRepeater) ...[
               ListTile(
                 leading: const Icon(Icons.radar, color: Colors.green),

lib/screens/discovery_screen.dart

@@ -218,6 +218,8 @@ class _DiscoveryScreenState extends State<DiscoveryScreen> {
     Contact contact,
     MeshCoreConnector connector,
   ) async {
+    final blockService = context.read<BlockService>();
+    final isBlocked = blockService.isBlocked(contact.publicKeyHex);
     final action = await showModalBottomSheet<String>(
       context: context,
       showDragHandle: true,
@@ -237,6 +239,16 @@ class _DiscoveryScreenState extends State<DiscoveryScreen> {
                 title: Text(l10n.discoveredContacts_copyContact),
                 onTap: () => Navigator.of(sheetContext).pop('copy_contact'),
               ),
+              ListTile(
+                leading: Icon(
+                  isBlocked ? Icons.check_circle_outline : Icons.block,
+                  color: isBlocked ? null : Colors.red.shade700,
+                ),
+                title: Text(isBlocked ? l10n.block_unblock : l10n.block_block),
+                onTap: () => Navigator.of(
+                  sheetContext,
+                ).pop(isBlocked ? 'unblock' : 'block'),
+              ),
               ListTile(
                 leading: const Icon(Icons.delete),
                 title: Text(l10n.discoveredContacts_deleteContact),
@@ -267,6 +279,12 @@ class _DiscoveryScreenState extends State<DiscoveryScreen> {
       case 'delete_contact':
         connector.removeDiscoveredContact(contact);
         break;
+      case 'block':
+        await blockService.block(contact.publicKeyHex);
+        break;
+      case 'unblock':
+        await blockService.unblock(contact.publicKeyHex);
+        break;
     }
   }