fix(podcasts): serialize explicit as a real boolean in API responses

SQLite has no boolean type, so raw rows return explicit as 0/1. The
podcast edit form round-trips whatever GET /api/podcasts/:id sends it,
and the update schema requires z.boolean() — so saving any change
without also touching the explicit checkbox failed validation with
"Expected boolean, received number".

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

server/src/app.test.ts

@@ -171,6 +171,23 @@ describe('podcasts, episodes, feed', () => {
     expect(res.statusCode).toBe(201);
     podcastId = res.json().id;
     expect(res.json().podcast_guid).toMatch(/^[0-9a-f-]{36}$/);
+    expect(res.json().explicit).toBe(false); // not the raw SQLite 0/1
+  });
+
+  it('lets the edit form round-trip a fetched podcast unmodified (regression: explicit came back as 0/1, not a bool)', async () => {
+    const fetched = await app.inject({ method: 'GET', url: `/api/podcasts/${podcastId}`, headers: { cookie } });
+    expect(fetched.json().explicit).toBe(false);
+
+    const { episodes: _episodes, feed_url: _feedUrl, ...editForm } = fetched.json();
+    const res = await app.inject({
+      method: 'PUT',
+      url: `/api/podcasts/${podcastId}`,
+      headers: { cookie },
+      payload: editForm,
+    });
+    expect(res.statusCode).toBe(200);
+    expect(res.json().lightning_address).toBe('tester@getalby.com');
+    expect(res.json().explicit).toBe(false);
   });
 
   it('registers an episode after verifying the blob on blossom', async () => {