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>

RenderWorker/VFXReviewWorker/Program.cs

@@ -0,0 +1,30 @@
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using VFXReviewWorker;
+
+// VFXReview RenderWorker (RenderPipeline2 §7) — Windows service driving
+// aerender.exe on artist workstations / render nodes. All state flows through
+// /api/ext/* with API-key auth; the worker never touches the database.
+//
+// Run interactively for debugging:  VFXReviewWorker.exe [path\to\config.json]
+// Install as a service:             see RenderWorker/README.md
+
+var configPath = args.FirstOrDefault(a => !a.StartsWith('-'));
+var options = WorkerOptions.Load(configPath);
+
+// Positional args (config path) are consumed above and deliberately not
+// forwarded — the command-line configuration provider rejects bare tokens.
+var builder = Host.CreateApplicationBuilder();
+builder.Services.AddWindowsService(o => o.ServiceName = "VFXReviewRenderWorker");
+builder.Logging.AddProvider(new FileLoggerProvider());
+
+builder.Services.AddSingleton(options);
+builder.Services.AddSingleton<ApiClient>();
+builder.Services.AddSingleton<ReportSpooler>();
+builder.Services.AddSingleton<AerenderRunner>();
+builder.Services.AddSingleton<PreviewStage>();
+builder.Services.AddSingleton<JobExecutor>();
+builder.Services.AddHostedService<WorkerService>();
+
+await builder.Build().RunAsync();