Implement the rule model and parser for global rules

[Matographo]

Summary

Add support for global rule definitions, validation, and normalized internal rule representation.

Why

Rules are a core abstraction and need a stable model before selector-based precedence can be implemented.

Acceptance Criteria

• Global rules parse consistently
• Invalid rule definitions fail clearly
• Rule records are ready for precedence resolution

Dependencies

• Depends on Specify CLI behavior, inspection commands, and exit codes #2
• Depends on Create the base project structure for CLI, engine, parser, evaluator, and config #3