Render and navigate [[wikilink]] syntax in notes

- Add WikilinkSyntax (InlineSyntax) that parses [[Note Title]] into
  anchor elements with a wikilink:// href
- wikilinkExtensionSet extends GFM with this syntax; shared by detail
  view and edit preview so rendering is consistent
- NoteDetailScreen handles onTapLink: wikilink:// hrefs look up the
  target note by title (case-insensitive) and push its detail route;
  unresolved links show a "Note not found" snackbar
- Add markdown as an explicit dependency (was previously transitive)

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

lib/screens/notes/note_detail_screen.dart

@@ -4,6 +4,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
 import '../../core/constants.dart';
+import '../../core/wikilink_syntax.dart';
 import '../../providers/notes_provider.dart';
 
 class NoteDetailScreen extends ConsumerWidget {
@@ -15,6 +16,22 @@ class NoteDetailScreen extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final noteAsync = ref.watch(noteDetailProvider(noteId));
+    final allNotes = ref.watch(notesProvider).valueOrNull ?? [];
+
+    void navigateByTitle(String title) {
+      final matches = allNotes.where(
+        (n) => n.title.toLowerCase() == title.toLowerCase(),
+      );
+      if (matches.isNotEmpty) {
+        context.push(
+          Routes.noteDetail.replaceFirst(':id', '${matches.first.id}'),
+        );
+      } else {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(content: Text('Note not found: "$title"')),
+        );
+      }
+    }
 
     return Scaffold(
       appBar: AppBar(
@@ -71,6 +88,13 @@ class NoteDetailScreen extends ConsumerWidget {
         data: (note) => Markdown(
           data: note.body,
           selectable: true,
+          extensionSet: wikilinkExtensionSet,
+          onTapLink: (text, href, _) {
+            if (href == null) return;
+            if (href.startsWith('wikilink://')) {
+              navigateByTitle(Uri.decodeComponent(href.substring(11)));
+            }
+          },
         ),
       ),
     );

lib/screens/notes/note_edit_screen.dart

@@ -4,6 +4,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
 import '../../core/exceptions.dart';
+import '../../core/wikilink_syntax.dart';
 import '../../providers/api_client_provider.dart';
 import '../../providers/notes_provider.dart';
 
@@ -149,7 +150,10 @@ class _NoteEditScreenState extends ConsumerState<NoteEditScreen> {
                     const Divider(),
                     Expanded(
                       child: _preview
-                          ? Markdown(data: _contentController.text)
+                          ? Markdown(
+                              data: _contentController.text,
+                              extensionSet: wikilinkExtensionSet,
+                            )
                           : Padding(
                               padding:
                                   const EdgeInsets.symmetric(horizontal: 16),