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.Tests/PathMapperTests.cs

@@ -0,0 +1,87 @@
+using VFXReviewWorker;
+using Xunit;
+
+namespace VFXReviewWorker.Tests;
+
+public class PathMapperTests
+{
+    private static PathMapper Mapper(params (string from, string to)[] maps) =>
+        new(maps.Select(m => new PathMapping { From = m.from, To = m.to }));
+
+    [Fact]
+    public void MapsUncToDriveLetter()
+    {
+        var mapper = Mapper(("//SAN/", "S:/"));
+        Assert.Equal(@"S:\renders\UNG_S1\106\shot\v004", mapper.Map("//SAN/renders/UNG_S1/106/shot/v004"));
+    }
+
+    [Fact]
+    public void MapsBackslashInputToo()
+    {
+        var mapper = Mapper(("//SAN/", "S:/"));
+        Assert.Equal(@"S:\projects\a.aep", mapper.Map(@"\\SAN\projects\a.aep"));
+    }
+
+    [Fact]
+    public void CaseInsensitiveMatch()
+    {
+        var mapper = Mapper(("//SAN/", "S:/"));
+        Assert.Equal(@"S:\x", mapper.Map("//san/x"));
+    }
+
+    [Fact]
+    public void FirstMatchingMappingWins()
+    {
+        var mapper = Mapper(("//SAN/renders/", "R:/"), ("//SAN/", "S:/"));
+        Assert.Equal(@"R:\a", mapper.Map("//SAN/renders/a"));
+        Assert.Equal(@"S:\projects\a", mapper.Map("//SAN/projects/a"));
+    }
+
+    [Fact]
+    public void UnmappedPathPassesThroughWithLocalSeparators()
+    {
+        var mapper = Mapper(("//SAN/", "S:/"));
+        Assert.Equal(@"D:\local\thing", mapper.Map("D:/local/thing"));
+    }
+}
+
+public class PrepareOutputDirTests
+{
+    [Fact]
+    public void ClearsOnlyFilesMatchingPatternPrefix()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "vfxr-test-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        try
+        {
+            File.WriteAllText(Path.Combine(dir, "SHOT_cmp_TT_v004.1001.exr"), "old");
+            File.WriteAllText(Path.Combine(dir, "SHOT_cmp_TT_v004.1002.exr"), "old");
+            File.WriteAllText(Path.Combine(dir, "unrelated-notes.txt"), "keep me");
+
+            AerenderRunner.PrepareOutputDir(dir, "SHOT_cmp_TT_v004.[####].exr");
+
+            Assert.False(File.Exists(Path.Combine(dir, "SHOT_cmp_TT_v004.1001.exr")));
+            Assert.False(File.Exists(Path.Combine(dir, "SHOT_cmp_TT_v004.1002.exr")));
+            Assert.True(File.Exists(Path.Combine(dir, "unrelated-notes.txt")));
+        }
+        finally
+        {
+            Directory.Delete(dir, recursive: true);
+        }
+    }
+
+    [Fact]
+    public void CreatesMissingDirectory()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "vfxr-test-" + Guid.NewGuid().ToString("N"), "v001");
+        try
+        {
+            AerenderRunner.PrepareOutputDir(dir, "X.[####].exr");
+            Assert.True(Directory.Exists(dir));
+        }
+        finally
+        {
+            Directory.Delete(Path.GetDirectoryName(dir)!, recursive: true);
+        }
+    }
+}