match the appSubUrl shape Gitea actually emits

The regex expected JSON — "appSubUrl":"…" — and Gitea emits a JavaScript object
literal: unquoted key, single quotes, `appSubUrl: ''`. So the single
highest-value rewrite in this file silently did nothing on every real page,
while every attribute around it rewrote perfectly.

The test used the shape I guessed rather than the shape Gitea produces, which
is why it passed. Now covers both, with the real form taken verbatim from a
live response, and asserts the quote style survives — swapping it would stop
the literal parsing.

sidecar/rewrite.test.ts

@@ -40,6 +40,17 @@ describe('appSubUrl — the line that makes Gitea correct itself', () => {
   test('an existing subpath is replaced, not appended to', () => {
     expect(rewriteAppSubUrl('{"appSubUrl":"/git"}', BASE)).toBe(`{"appSubUrl":"${BASE}"}`);
   });
+
+  // The shape Gitea ACTUALLY emits — a JavaScript object literal, unquoted key, single quotes. The first
+  // version of this only matched the JSON form, so it silently did nothing on every real page while the
+  // attributes around it rewrote perfectly. Taken verbatim from a live response.
+  test('the JS object-literal form Gitea really emits', () => {
+    const real = "window.config = {\n  appUrl: 'https://gitea.officer.dev/',\n  appSubUrl: '',\n};";
+    const out = rewriteAppSubUrl(real, BASE);
+    expect(out).toContain(`appSubUrl: '${BASE}'`);
+    // The quote style is preserved, or the literal stops parsing.
+    expect(out).not.toContain(`appSubUrl: "${BASE}"`);
+  });
 });
 
 describe('absolute URLs built from ROOT_URL', () => {