feat: enforce playout schema version

[jasongdove]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces schema versioning and validation for playout files. It defines a SchemaVersion struct, parses the version URI from the playout JSON, and validates it against the supported schema version before parsing the full playout structure. A review comment points out an inconsistency in the UnsupportedSchemaVersion error message, where the found version is a full URI but the expected version is formatted as a short version string, and suggests formatting the expected version as a full URI for consistency.