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/WorkerOptions.cs

@@ -0,0 +1,79 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace VFXReviewWorker;
+
+/// <summary>
+/// Machine-local config (RenderPipeline2 §7.8) — deliberately minimal;
+/// everything tunable lives in server SystemConfig and arrives via E6.
+/// Default path: C:\ProgramData\VFXReviewWorker\config.json
+/// </summary>
+public sealed class WorkerOptions
+{
+    public string ServerUrl { get; set; } = "";
+    public string ApiKey { get; set; } = "";
+    public string MachineName { get; set; } = Environment.MachineName;
+    public string AerenderPath { get; set; } = @"C:\Program Files\Adobe\Adobe After Effects 2026\Support Files\aerender.exe";
+    /// <summary>AfterFX.com — the console AE used for the headless preview build. Defaults beside aerender.</summary>
+    public string? AfterFxPath { get; set; }
+    /// <summary>vfxr_build_preview.jsx — defaults to scripts\ beside the worker exe.</summary>
+    public string? PreviewScriptPath { get; set; }
+    public string? FfmpegPath { get; set; }
+    public string? OiiotoolPath { get; set; }
+    public List<PathMapping> PathMappings { get; set; } = new();
+    public string WorkerVersion { get; set; } = "1.0.0";
+    public string? AeVersion { get; set; }
+
+    public static string DataDir =>
+        Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData), "VFXReviewWorker");
+
+    public static string DefaultConfigPath => Path.Combine(DataDir, "config.json");
+    public static string LogsDir => Path.Combine(DataDir, "logs");
+    public static string SpoolDir => Path.Combine(DataDir, "spool");
+    public static string ScratchDir => Path.Combine(DataDir, "scratch");
+    public static string StateFilePath => Path.Combine(DataDir, "current-job.json");
+
+    /// <summary>AfterFX.com sits beside aerender.exe in a standard AE install.</summary>
+    public string ResolveAfterFxPath()
+    {
+        if (!string.IsNullOrWhiteSpace(AfterFxPath)) return AfterFxPath;
+        var dir = Path.GetDirectoryName(AerenderPath);
+        return dir is null ? "AfterFX.com" : Path.Combine(dir, "AfterFX.com");
+    }
+
+    public string ResolvePreviewScriptPath()
+    {
+        if (!string.IsNullOrWhiteSpace(PreviewScriptPath)) return PreviewScriptPath;
+        return Path.Combine(AppContext.BaseDirectory, "scripts", "vfxr_build_preview.jsx");
+    }
+
+    public static WorkerOptions Load(string? path = null)
+    {
+        path ??= DefaultConfigPath;
+        if (!File.Exists(path))
+        {
+            throw new FileNotFoundException(
+                $"Worker config not found at {path}. Create it with serverUrl, apiKey and machineName (see RenderWorker/README.md).");
+        }
+        var json = File.ReadAllText(path);
+        var opts = JsonSerializer.Deserialize<WorkerOptions>(json, JsonOpts)
+                   ?? throw new InvalidOperationException($"Could not parse {path}");
+        if (string.IsNullOrWhiteSpace(opts.ServerUrl)) throw new InvalidOperationException("config.json: serverUrl is required");
+        if (string.IsNullOrWhiteSpace(opts.ApiKey)) throw new InvalidOperationException("config.json: apiKey is required");
+        if (string.IsNullOrWhiteSpace(opts.MachineName)) opts.MachineName = Environment.MachineName;
+        return opts;
+    }
+
+    public static readonly JsonSerializerOptions JsonOpts = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+    };
+}
+
+public sealed class PathMapping
+{
+    public string From { get; set; } = "";
+    public string To { get; set; } = "";
+}