[P2.3-T01] Enhance cch explain rule command

[RichardHightower]

Task: Enhance cch explain rule command

Phase: 2.3 - CLI Enhancements
Estimated: 0.5 day
File: cch_cli/src/cli/explain.rs
Depends on: P2.1-T03

Description

Display governance fields in cch explain rule output.

Acceptance Criteria

• Display mode (with default indicator)
• Display priority (with default indicator)
• Display full metadata block
• Format output for readability
• Add --json flag for structured output

Output Format

Rule: <name>
Event: <event_type>
Mode: <mode> (default: enforce)
Priority: <priority> (default: 0)

Matchers:
  tools: [...]
  extensions: [...]

Action:
  <action_type>: <action_config>

Metadata:
  author: <author>
  created_by: <created_by>
  reason: <reason>
  confidence: <confidence>
  last_reviewed: <date>
  ticket: <ticket>
  tags: [...]

[RichardHightower]

Completed in PR #72