internal_links: Add Variable realmUrlWithSlash to add '/'

Updates the URL construction to include a trailing slash
before the fragment identifier. This ensures that the URL
is properly formatted and makes the url linkified.

Fixes: #845

Author: satyam372

lib/model/internal_link.dart

@@ -96,7 +96,11 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
     fragment.write('/near/$nearMessageId');
   }
 
-  return store.realmUrl.replace(fragment: fragment.toString());
+  final realmUrlWithSlash = store.realmUrl.path.endsWith('/')
+      ? store.realmUrl
+      : store.realmUrl.replace(path: '${store.realmUrl.path}/');
+
+  return realmUrlWithSlash.replace(fragment: fragment.toString());
 }
 
 /// A [Narrow] from a given URL, on `store`'s realm.

test/widgets/action_sheet_test.dart

@@ -553,6 +553,21 @@ void main() {
     });
   });
 
+
+  group('narrowLink URL generation tests', () {
+
+    testWidgets('Full Url Testing', (tester) async {
+      final message = eg.streamMessage();
+      final narrow = TopicNarrow.ofMessage(message);
+      await setupToMessageActionSheet(tester, message: message, narrow: narrow);
+      final store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
+      final generatedLink = narrowLink(store, narrow, nearMessageId: message.id).toString();
+      const expectedPrefix = 'https://chat.example/#narrow/stream/123-stream-123/topic';
+      final truncatedLink = generatedLink.split('/example').first;
+      check(truncatedLink).equals(expectedPrefix);
+    });
+  });
+
   group('ShareButton', () {
     // Tests should call this.
     MockSharePlus setupMockSharePlus() {