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>

components/layout/Sidebar.tsx

@@ -21,6 +21,7 @@ import {
   CloudUpload,
   Clapperboard,
   LayoutGrid,
+  Server,
 } from 'lucide-react';
 import { useState } from 'react';
 import { useSession } from 'next-auth/react';
@@ -32,6 +33,7 @@ const navItems = [
   { href: '/shot-status', label: 'Shot Status', icon: BarChart2, hideForClient: true },
   { href: '/playlist', label: 'Playlist', icon: ListVideo, hideForClient: true },
   { href: '/tasks', label: 'My Tasks', icon: ListTodo, hideForClient: true },
+  { href: '/pipeline', label: 'Pipeline', icon: Server, hideForClient: true },
   { href: '/shoot-log', label: 'Shot Log', icon: Clapperboard, supervisorOnly: true },
   { href: '/storyboard', label: 'Storyboard', icon: LayoutGrid, supervisorOnly: true },
   { href: '/schedule', label: 'Schedule', icon: CalendarRange, adminOnly: true },