[P2.1-T03] Extend Rule struct with governance fields

[RichardHightower]

Task: Extend Rule struct with governance fields

Phase: 2.1 - Core Governance
Estimated: 0.5 day
File: cch_cli/src/models/mod.rs
Depends on: P2.1-T01, P2.1-T02

Description

Add mode, priority, and metadata fields to the Rule struct.

Acceptance Criteria

• Add mode: Option<PolicyMode> field to Rule
• Add priority: Option<i32> field to Rule
• Add metadata: Option<RuleMetadata> field to Rule
• Use #[serde(default)] for backward compatibility
• Update existing tests to verify backward compatibility
• Add new tests for parsing rules with governance fields

Backward Compatibility

Existing v1.0 configs MUST continue to parse without changes. All new fields use Option<T> with sensible defaults.

[RichardHightower]

Completed in PR #72