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)/projects/[id]/shots/[shotId]/page.tsx

@@ -34,6 +34,7 @@ import {
 import { Input } from "@/components/ui/input";
 import type { ShotWithDetails } from "@/types";
 import { ShotSettingsTab } from "@/components/shots/ShotSettingsTab";
+import { ShotExportsTab } from "@/components/shots/ShotExportsTab";
 import { FootageViewer } from "@/components/shots/FootageViewer";
 import { HighResUploadDialog } from "@/components/shots/HighResUploadDialog";
 import { duplicateShot, internallyApproveShot, shareWithClient, unshareFromClient, unapproveShot, updateShotVersion } from "@/actions/shots";
@@ -89,7 +90,7 @@ export default function ShotDetailPage() {
   const [isDuplicating, setIsDuplicating] = useState(false);
   const [isActioning, setIsActioning] = useState(false);
   const [highResDialogOpen, setHighResDialogOpen] = useState(false);
-  const [activeTab, setActiveTab] = useState<"tasks" | "reviews" | "footage" | "settings">("tasks");
+  const [activeTab, setActiveTab] = useState<"tasks" | "reviews" | "footage" | "exports" | "settings">("tasks");
   const [editingVersion, setEditingVersion] = useState(false);
   const [versionInput, setVersionInput] = useState("");
   const [savingVersion, setSavingVersion] = useState(false);
@@ -543,6 +544,18 @@ export default function ShotDetailPage() {
             <Video className="h-4 w-4" />
             Footage
           </button>
+          <button
+            onClick={() => setActiveTab("exports")}
+            className={cn(
+              "flex items-center gap-2 px-4 py-2.5 text-sm font-medium border-b-2 transition-colors -mb-px",
+              activeTab === "exports"
+                ? "border-amber-500 text-amber-400"
+                : "border-transparent text-zinc-500 hover:text-zinc-300"
+            )}
+          >
+            <Film className="h-4 w-4" />
+            Exports
+          </button>
           {canManage && (
             <button
               onClick={() => setActiveTab("settings")}
@@ -658,6 +671,8 @@ export default function ShotDetailPage() {
           />
         )}
 
+        {activeTab === "exports" && <ShotExportsTab shotId={shot.id} />}
+
         {activeTab === "settings" && canManage && (
           <ShotSettingsTab shot={shot} artists={artists} onSaved={fetchShot} />
         )}