fix(favorites): normalize scheme-less URLs so favicons resolve

A favorite entered as a bare host ("ctl.de") passed @IsUrl() but had no
scheme, so `new URL()` threw inside icon discovery and it silently fell
back to a relative "/favicon.ico" — which 502'd through the icon proxy
and left the widget showing the first-letter placeholder ("C").

- add normalizeUrl() (prepend https:// when no scheme present)
- apply it in discoverFavoriteIconUrl and when storing the favorite url,
  so both the link and discovery use the normalized value
- on update, re-run discovery when the icon field is cleared, so editing
  a previously-broken favorite repairs its icon
- tests: normalizeUrl cases + end-to-end discovery (apple-touch extraction,
  scheme-less fallback stays absolute)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/src/favorites/icon-discovery.service.spec.ts

@@ -1,5 +1,9 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
-import { IconDiscoveryService, isPublicHttpUrl } from './icon-discovery.service';
+import {
+  IconDiscoveryService,
+  isPublicHttpUrl,
+  normalizeUrl,
+} from './icon-discovery.service';
 
 function mockResponse(options: {
   contentType?: string;
@@ -46,6 +50,71 @@ describe('isPublicHttpUrl', () => {
   });
 });
 
+describe('normalizeUrl', () => {
+  it('prepends https:// to a scheme-less host', () => {
+    expect(normalizeUrl('ctl.de')).toBe('https://ctl.de');
+    expect(normalizeUrl('www.ctl.de/path')).toBe('https://www.ctl.de/path');
+  });
+
+  it('leaves an existing scheme untouched', () => {
+    expect(normalizeUrl('http://ctl.de')).toBe('http://ctl.de');
+    expect(normalizeUrl('https://ctl.de')).toBe('https://ctl.de');
+  });
+
+  it('trims surrounding whitespace', () => {
+    expect(normalizeUrl('  ctl.de  ')).toBe('https://ctl.de');
+  });
+
+  it('returns empty string unchanged', () => {
+    expect(normalizeUrl('   ')).toBe('');
+  });
+});
+
+describe('IconDiscoveryService.discoverFavoriteIconUrl', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it('extracts the apple-touch-icon from page HTML', async () => {
+    const html = `<html><head>
+      <link rel="icon" href="https://ctl.de/fav-32.jpg" sizes="32x32" />
+      <link rel="apple-touch-icon" href="https://ctl.de/apple-180.jpg" />
+    </head></html>`;
+    vi.stubGlobal(
+      'fetch',
+      vi.fn().mockResolvedValue({
+        ok: true,
+        status: 200,
+        headers: {
+          get: (n: string) =>
+            n.toLowerCase() === 'content-type'
+              ? 'text/html; charset=utf-8'
+              : null,
+        },
+        text: async () => html,
+      }),
+    );
+
+    const service = new IconDiscoveryService();
+    // Public IP avoids a real DNS lookup in the SSRF guard.
+    const icon = await service.discoverFavoriteIconUrl('http://8.8.8.8');
+
+    expect(icon).toBe('https://ctl.de/apple-180.jpg');
+  });
+
+  it('normalizes a scheme-less URL so the fallback is absolute, not "/favicon.ico"', async () => {
+    // fetch fails → discovery falls back. The fallback must be an absolute
+    // https origin URL, not the broken relative path that produced the bug.
+    vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('network')));
+
+    const service = new IconDiscoveryService();
+    const icon = await service.discoverFavoriteIconUrl('ctl.de');
+
+    expect(icon).toBe('https://ctl.de/favicon.ico');
+  });
+});
+
 describe('IconDiscoveryService.fetchIconBytes', () => {
   afterEach(() => {
     vi.restoreAllMocks();