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/(dashboard)/pipeline/status-colors.ts

@@ -0,0 +1,33 @@
+/** Shared status→style maps for the pipeline pages. */
+
+export const EXPORT_STATUS_STYLES: Record<string, string> = {
+  QUEUED: "bg-zinc-500/15 text-zinc-300 border-zinc-500/30",
+  RENDERING: "bg-blue-500/15 text-blue-400 border-blue-500/30",
+  RENDER_FAILED: "bg-red-500/15 text-red-400 border-red-500/30",
+  VALIDATING: "bg-sky-500/15 text-sky-400 border-sky-500/30",
+  VALIDATION_FAILED: "bg-red-500/15 text-red-400 border-red-500/30",
+  GENERATING_PREVIEW: "bg-indigo-500/15 text-indigo-400 border-indigo-500/30",
+  PREVIEW_FAILED: "bg-red-500/15 text-red-400 border-red-500/30",
+  READY_FOR_QC: "bg-amber-500/15 text-amber-400 border-amber-500/30",
+  QC_FAILED: "bg-red-500/15 text-red-400 border-red-500/30",
+  READY_FOR_DELIVERY: "bg-green-500/15 text-green-400 border-green-500/30",
+  PACKAGED: "bg-emerald-500/15 text-emerald-400 border-emerald-500/30",
+  DELIVERED: "bg-emerald-500/15 text-emerald-300 border-emerald-500/30",
+  SUPERSEDED: "bg-zinc-500/10 text-zinc-500 border-zinc-600/30",
+  ARCHIVED: "bg-zinc-500/10 text-zinc-500 border-zinc-600/30",
+  CANCELLED: "bg-zinc-500/10 text-zinc-500 border-zinc-600/30",
+};
+
+export const FAILED_STATUSES = ["RENDER_FAILED", "VALIDATION_FAILED", "PREVIEW_FAILED", "QC_FAILED"];
+export const ACTIVE_STATUSES = ["QUEUED", "RENDERING", "VALIDATING", "GENERATING_PREVIEW"];
+
+export function statusLabel(status: string): string {
+  return status.replaceAll("_", " ");
+}
+
+export function formatEta(seconds: number | null | undefined): string {
+  if (seconds == null || seconds <= 0) return "—";
+  const m = Math.floor(seconds / 60);
+  const s = Math.round(seconds % 60);
+  return m > 0 ? `${m}m ${s}s` : `${s}s`;
+}