fix(producer): accept plain integer fps in createRenderJob

The rational `Fps = { num, den }` refactor in 5dcc89c broke callers
passing `fps: 30` (the form documented in every code example and used
by external consumers). FFmpeg received `undefined/undefined` as the
framerate, causing a cryptic exit-code error.

Add `FpsInput = number | Fps` and `toFps()` normalizer in
@hyperframes/core. `createRenderJob` now accepts both forms —
plain integers are promoted to `{ num, den: 1 }` at the boundary;
`RenderConfig.fps` stays strict `Fps` internally so no downstream
code changes.

Also fixes the producer and engine docs, which showed phantom
`input`/`output` fields on `createRenderJob` and a wrong
`executeRenderJob(job)` signature (missing `projectDir`/`outputPath`
args).

Closes #1031

packages/core/src/index.ts

@@ -12,6 +12,7 @@ export type {
   MediaElementType,
   CanvasResolution,
   Fps,
+  FpsInput,
   FpsParseResult,
   MediaFile,
   CompositionAPI,
@@ -42,6 +43,7 @@ export {
   normalizeResolutionFlag,
   parseFps,
   parseFpsWithDefault,
+  toFps,
   fpsToNumber,
   fpsToFfmpegArg,
   TIMELINE_COLORS,