Module parser 

Playbook YAML parsing and structural validation (PB-001)

Parses YAML into typed Playbook and validates structural constraints:

• version must be “1.0”
• stages must have non-empty cmd
• after references must point to valid stage names
• param template references must resolve

Functions

parse_playbook

Parse a playbook from a YAML string

parse_playbook_file

Parse a playbook from a YAML file path

validate_playbook

Validate a parsed playbook, returning warnings for non-fatal issues