Service: job event stream, async in-memory backend, preview routes

Ported from PR #15 (packages-side surface only; the fork's dev UI page is
intentionally dropped - the API surface is the product):
- job_events table + repository, worker emits stage transitions, additive
  GET /v1/clones/:id/events polling route. The fork's hand-written
  migration was never registered in Drizzle's journal (it silently never
  applied); regenerated properly via drizzle-kit from schema.ts with the
  (job_id, seq) index declared, and verified against a live Postgres
- In-memory backend moves to the documented enqueue-202 + poll contract
  with single-flight BUSY guard; POST honors backend httpStatus
- app-preview static serving routes; the preview BUILD half is deferred
  until the compiler exports buildApp/DEFAULT_HARNESS_DIR - routes 404
  cleanly until then
- preview option threaded through core types; cache key intentionally
  unchanged while the flag is inert

All workspaces typecheck; api 18/18, core 13/13, worker 1/1 pass;
migration verified applying (table + index + FK) on postgres:16.

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

packages/api/test/app.fixture.test.ts

@@ -26,13 +26,25 @@ describe("POST /v1/clones (real clone, served fixture)", { skip: hasChromium() ?
       headers: { "content-type": "application/json" },
       body: JSON.stringify({ url: server.url + "/components.html", options: { interactions: false, components: true, motion: false } }),
     });
-    assert.equal(res.status, 200);
-    const body = await res.json();
-    assert.equal(body.status, "succeeded");
-    assert.ok(body.files["src/app/page.tsx"], "has page.tsx");
-    assert.equal(body.files["src/app/page.tsx"].type, "text");
-    assert.ok(body.files["package.json"], "has package.json");
-    assert.ok(body.capture.nodeCount > 0);
-    assert.equal(body.capture.blocked, false);
+    assert.equal(res.status, 202);
+    const queued = await res.json();
+    let body: Record<string, unknown> | undefined;
+    for (let i = 0; i < 600; i++) {
+      const view = await (await app.request(`/v1/clones/${queued.jobId}`)).json();
+      if (view.status === "succeeded") {
+        body = await (await app.request(`/v1/clones/${queued.jobId}/result`)).json();
+        break;
+      }
+      if (view.status === "failed") assert.fail(view.error);
+      await new Promise((r) => setTimeout(r, 50));
+    }
+    assert.ok(body);
+    const files = body!.files as Record<string, { type: string }>;
+    assert.equal(body!.status, "succeeded");
+    assert.ok(files["src/app/page.tsx"], "has page.tsx");
+    assert.equal(files["src/app/page.tsx"].type, "text");
+    assert.ok(files["package.json"], "has package.json");
+    assert.ok((body!.capture as { nodeCount: number }).nodeCount > 0);
+    assert.equal((body!.capture as { blocked: boolean }).blocked, false);
   });
 });