feat: add Gemini and Spartan protocol support

app/lib/application/pages/certificates_page.dart

@@ -0,0 +1,82 @@
+import '../../database/database.dart';
+import '../../l10n/strings.dart';
+import '../../mews/document.dart';
+import 'mews_urls.dart';
+import 'page_blocks.dart';
+
+/// The reader's certificates, worn as identities on Gemini sites that ask for
+/// one. An identity is added from a PEM file, renamed in place, and removed
+/// in a second step when it is worn anywhere, because the sites that know it
+/// lose it with the removal.
+Future<MewsPage> buildCertificatesPage(
+  Uri url, {
+  required MewsDatabase db,
+  required Strings strings,
+}) async {
+  final title = strings.t('certificates-title');
+  final held = await db.allClientCertificates();
+
+  final body = <MewsBlock>[
+    ...chrome(title: title, current: url, strings: strings),
+    ParagraphBlock([
+      MewsLink(MewsUrls.action('import-certificate'), [
+        MewsText(strings.t('certificates-add')),
+      ]),
+    ]),
+  ];
+
+  // Removing an identity takes a second step, like clearing history: the
+  // sites it is worn at stop seeing it too, and that cannot be undone.
+  final forgetting = int.tryParse(url.queryParameters['forget'] ?? '');
+  final row = forgetting == null ? null : await db.clientCertificate(forgetting);
+  if (row != null) {
+    body.addAll([
+      HeadingBlock(2, [MewsText(row.name)]),
+      ParagraphBlock([MewsText(strings.t('certificates-delete-confirm'))]),
+      ...linkLine([
+        action(
+            MewsUrls.action('delete-certificate', {'id': '${row.id}'}),
+            strings.t('certificates-delete-yes')),
+        action(MewsUrls.certificates, strings.t('certificates-delete-no')),
+      ]),
+    ]);
+  }
+
+  if (held.isEmpty) {
+    body.add(ParagraphBlock([MewsText(strings.t('certificates-empty'))]));
+  } else {
+    final rows = <MewsListItem>[];
+    for (final certificate in held) {
+      final worn = await db.bindingsOf(certificate.id);
+      rows.add(MewsListItem([
+        ParagraphBlock([
+          MewsEmphasis(EmphasisStyle.strong, [MewsText(certificate.name)]),
+          if (worn.isNotEmpty) ...[
+            const MewsLineBreak(),
+            MewsEmphasis(
+              EmphasisStyle.emphasis,
+              [
+                MewsText(worn
+                    .map((host) => strings.t('certificates-bound-to', {'host': host}))
+                    .join(actionSeparator)),
+              ],
+            ),
+          ],
+          const MewsLineBreak(),
+          MewsLink(MewsUrls.page(url, {'forget': '${certificate.id}'}),
+              [MewsText(strings.t('certificates-remove'))]),
+        ]),
+        textForm(
+          action: MewsUrls.action('rename-certificate', {'id': '${certificate.id}'}),
+          field: 'name',
+          label: strings.t('certificates-rename-label'),
+          submitLabel: strings.t('certificates-rename-submit'),
+          value: certificate.name,
+        ),
+      ]));
+    }
+    body.add(itemList(rows));
+  }
+
+  return internalPage(url: url, title: title, body: body, strings: strings);
+}