feat(pipeline): render queue, worker service and automated preview generation

One "Queue Export" click now renders the EXR sequence, then rebuilds the shot
headlessly with the studio slate/overlay template to produce the delivery MOV
and review MP4. Implements RenderPipeline2 phases 1-2 plus the preview stage.

Server:
- New models Export, RenderJob, ExportEvent, Machine, WorkerHeartbeat, plus
  Project.deliveryConfig and per-submission slate fields (Export.vfxScope,
  Export.submissionNote, inherited from the shot's previous export).
  Both migrations are purely additive; no existing column is touched.
- lib/render-pipeline: server-enforced state machine, transactional version
  increment with supersede, atomic FOR UPDATE SKIP LOCKED claim gated by
  machine availability windows, and a lease reaper run from instrumentation.ts.
- /api/ext/* endpoints for the panel and workers; session-auth mirrors under
  /api/render and /api/machines for the web UI.
- Pipeline pages: render queue, export detail, machine monitoring, plus an
  Exports tab on shot detail.

RenderWorker (.NET 8 Windows service, new):
- Registration, heartbeat as cancel channel, claim loop, aerender runner with
  progress parsing and stall watchdog, crash recovery and disk-spooled
  reporting that survives server downtime.
- Preview stage: headless AE assembles the preview comp into a throwaway AEP
  with both output modules queued, then a single aerender pass renders them.
  Preview jobs are not claimed while an interactive AE session is open, so an
  artist's project is never taken over.

AE panel: Queue Export with live status polling, urgent flag, retry, and the
VFX Scope / Submission Note fields. Every existing panel action is unchanged.

Preview chaining ships disabled behind SystemConfig preview.enabled.

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

app/api/render/queue/route.ts

@@ -0,0 +1,34 @@
+import { NextRequest, NextResponse } from "next/server";
+import { ExportStatus } from "@prisma/client";
+import { toErrorResponse } from "@/lib/render-pipeline/errors";
+import { requirePipelineUser } from "@/lib/render-pipeline/session-auth";
+import { listExports } from "@/lib/render-pipeline/exports";
+
+// ── GET /api/render/queue (E21) ──────────────────────────────────────────────
+//
+// Exports list for the Render Queue page. Optional filters: projectId,
+// episode, status; standard pagination. Defaults to all statuses so the queue
+// page can show history too — the UI filters live states client-side.
+
+export async function GET(req: NextRequest) {
+  try {
+    await requirePipelineUser();
+    const { searchParams } = new URL(req.url);
+    const status = searchParams.get("status") ?? undefined;
+    const result = await listExports({
+      projectId: searchParams.get("projectId") ?? undefined,
+      episode: searchParams.get("episode") ?? undefined,
+      shotId: searchParams.get("shotId") ?? undefined,
+      status:
+        status && (Object.values(ExportStatus) as string[]).includes(status)
+          ? (status as ExportStatus)
+          : undefined,
+      page: Number(searchParams.get("page") ?? "1") || 1,
+      limit: Number(searchParams.get("limit") ?? "50") || 50,
+    });
+    return NextResponse.json(result);
+  } catch (err) {
+    const { body, status } = toErrorResponse(err);
+    return NextResponse.json(body, { status });
+  }
+}