Composable Strategy Foundation (YAML, compile, choices)

[Muratich]

Implement P0 composable engine per design doc.

Scope:

• Parse YAML: params (type, default, choices, optimizable), series, rules
• Compile: validate, resolve ${params}, build Series DAG, compile predicates/rules
• describe_strategy("composable") → ParameterSpec with choices (maps to existing schema)
• get_optimize_spec() → grid from params where optimizable: true
• Register @register_strategy("composable")

Definition of Done:

• Invalid YAML/config → clear errors at compile time
• Unit tests: parse, compile, choices validation
• config/param_presets.yaml + preset resolution (choices: preset:ma_long)
• Design doc §1.6 example runs at compile level