feat: add video frame format render option (#1481)

* feat: add video frame format render option

* refactor: single source of truth for video-frame-format allow-list

Addresses PR review (Via) on #1481: the ["auto","jpg","png"] set was
declared three times — render.ts (VIDEO_FRAME_FORMATS), server.ts
(inline includes), and renderConfigValidation.ts
(ALLOWED_VIDEO_FRAME_FORMATS) — three boundaries to update when a new
extraction format lands.

Hoist the constant + a reusable `isVideoFrameFormat` type guard into
@hyperframes/engine (where VideoFrameFormat is defined) and route all
three call sites through them. Behavior unchanged; also drops two
`as RenderConfig[...]` casts in favor of the guard (narrowing over
assertion, per repo TS conventions).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Xuelong Mu <xuelongmu@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/aws-lambda/src/sdk/validateConfig.test.ts

@@ -30,6 +30,7 @@ describe("validateDistributedRenderConfig", () => {
       maxParallelChunks: 16,
       runtimeCap: "lambda",
       hdrMode: "force-sdr",
+      videoFrameFormat: "png",
     };
     expect(validateDistributedRenderConfig(cfg)).toBe(cfg);
   });
@@ -92,6 +93,14 @@ describe("validateDistributedRenderConfig", () => {
       { ...VALID, bitrate: "fast" } satisfies SerializableDistributedRenderConfig,
       "config.bitrate",
     ],
+    [
+      "unsupported videoFrameFormat",
+      {
+        ...VALID,
+        videoFrameFormat: "webp",
+      } as unknown as SerializableDistributedRenderConfig,
+      "config.videoFrameFormat",
+    ],
     [
       "non-positive chunkSize",
       { ...VALID, chunkSize: 0 } satisfies SerializableDistributedRenderConfig,