The producer already supports `format: "png-sequence"` end-to-end (see
RenderConfig in renderOrchestrator.ts), but the CLI's VALID_FORMAT
validator rejects it before the flag reaches the producer. Surface it
the same way `mov` and `webm` are surfaced.
Behaviour:
- `--format png-sequence` accepted alongside mp4/webm/mov.
- Auto-output path uses no extension (FORMAT_EXT["png-sequence"] = "")
since the producer treats outputPath as a directory of frame_NNNNNN.png.
- `printRenderComplete` sums the contained file sizes when outputPath
is a directory, instead of reporting the platform-dependent inode
size.
- DockerRenderOptions.format type extended; existing buildDockerRunArgs
is unchanged because it forwards the string verbatim.
Tests:
- renderLocal forwards `format: "png-sequence"` to createRenderJob.
- buildDockerRunArgs propagates `--format png-sequence` to the
container.
Docs:
- Rendering guide: format flag table, format comparison table, new
"PNG sequence (no encoding)" section, "How it works" extended.
- CLI package docs: format flag table updated.
