feat: rework settings into the picked list, About and Storage & backup pages

The settings list now has the account card on top, title-case group
labels and 56 dp rows that show each pane's current value. About and
"About & Data" were one placeholder page with a letter logo, a fixed
name and a store link that pointed at GitHub releases.

- About: the real logo, the app name from app.config.js, the update
  state, a source link that a build can set with SOURCE_CODE_URL, and
  rows for the server, update checks (Android), open-source licences,
  privacy and a prefilled GitHub issue. iPhone updates link TestFlight.
- Storage & backup: usage card, offline mail, settings export/import
  and reset, and a Troubleshooting page for refresh and debug logging.
- Sender favicons moved to Appearance, like the webmail.
- The S/MIME and Plugins stub pages are gone; both are webmail plugins.

The licence list is generated by `scripts/generate-licences.mjs`.

scripts/generate-licences.mjs

@@ -0,0 +1,46 @@
+// Writes src/lib/licences.json: the libraries the app ships (the runtime
+// dependencies in package.json) with their licence, for Settings → About →
+// Open-source licences. Run after adding or upgrading a dependency:
+//
+//   node scripts/generate-licences.mjs
+//
+// The test in src/lib/__tests__/licences.test.ts fails when a dependency is
+// missing from the list.
+
+import { readFileSync, writeFileSync, existsSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const ROOT = join(dirname(fileURLToPath(import.meta.url)), '..');
+const pkg = JSON.parse(readFileSync(join(ROOT, 'package.json'), 'utf8'));
+
+// Code that isn't an npm dependency but ships in the app.
+const VENDORED = [
+  { name: 'Tabler Icons', version: '', license: 'MIT', url: 'https://tabler.io/icons' },
+];
+
+function repoUrl(meta) {
+  const repo = typeof meta.repository === 'string' ? meta.repository : meta.repository?.url;
+  const url = meta.homepage || repo || '';
+  return url
+    .replace(/^git\+/, '')
+    .replace(/^git:\/\//, 'https://')
+    .replace(/^github:/, 'https://github.com/')
+    .replace(/\.git$/, '')
+    .replace(/#.*$/, '');
+}
+
+const libraries = Object.keys(pkg.dependencies).sort().map((name) => {
+  const file = join(ROOT, 'node_modules', name, 'package.json');
+  if (!existsSync(file)) throw new Error(`${name} is not installed`);
+  const meta = JSON.parse(readFileSync(file, 'utf8'));
+  const license = typeof meta.license === 'string' ? meta.license : meta.license?.type ?? 'See package';
+  return { name, version: meta.version, license, url: repoUrl(meta) };
+});
+
+const out = {
+  app: { name: pkg.name, license: pkg.license },
+  libraries: [...libraries, ...VENDORED],
+};
+writeFileSync(join(ROOT, 'src', 'lib', 'licences.json'), `${JSON.stringify(out, null, 2)}\n`);
+console.log(`${out.libraries.length} libraries`);