Add frames_per_chunk and temporal_downsample_factor to pipeline schema metadata

[ryanontheinside]

Currently frames_per_chunk and temporal_downsample_factor are computed internally from pipeline block configs (num_frame_per_block × vae_temporal_downsample_factor) but aren't surfaced through the /api/v1/pipelines/schemas endpoint.

Exposing these in get_schema_with_metadata() would allow clients (e.g. ComfyUI nodepack) to display or use these values without hardcoding pipeline-specific constants.

Suggested approach

• Add frames_per_chunk and temporal_downsample_factor fields to the schema metadata dict returned by BasePipelineConfig.get_schema_with_metadata()
• Derive values from the pipeline's existing config (e.g. num_frame_per_block, vae_temporal_downsample_factor

[RUFFY-369]

yo @ryanontheinside are you working on this?