feat(website-shibumi): add dev server with mocked Resend client

Lets the newsletter subscribe/unsubscribe flow run in a browser without
credentials; calls log to the console. Production entry stays server.ts.

website-shibumi/scripts/dev-mock.ts

@@ -0,0 +1,49 @@
+/**
+ * Local dev server with a mocked Resend client, so the newsletter
+ * subscribe/unsubscribe flow can be exercised in a browser without real
+ * credentials. Every Resend call is logged to the console instead of
+ * hitting the API. Never used in production; the container runs server.ts.
+ *
+ *   bun scripts/dev-mock.ts            # http://localhost:8788
+ *   PORT=9000 bun scripts/dev-mock.ts
+ */
+import { createApp } from "../src/app";
+
+const mockEnv = { RESEND_API_KEY: "mock", RESEND_AUDIENCE_ID: "mock" };
+
+const app = createApp({
+  subscribe: {
+    env: mockEnv,
+    resendClient: {
+      contacts: {
+        async create(payload) {
+          console.log(`[mock resend] contacts.create ${payload.email}`);
+          return { error: null };
+        },
+      },
+      emails: {
+        async send(payload, options) {
+          console.log(
+            `[mock resend] emails.send to=${payload.to.join(",")} subject="${payload.subject}" idempotencyKey=${options?.idempotencyKey}`,
+          );
+          return { error: null };
+        },
+      },
+    },
+  },
+  unsubscribe: {
+    env: mockEnv,
+    resendClient: {
+      contacts: {
+        async remove(payload) {
+          console.log(`[mock resend] contacts.remove ${payload.email}`);
+          return { error: null };
+        },
+      },
+    },
+  },
+});
+
+const port = Number(process.env.PORT ?? 8788);
+Bun.serve({ port, fetch: app.fetch });
+console.log(`website-shibumi (mock Resend) listening on http://localhost:${port}`);