refactor: extract skills from commands across 8 plugins

Refactored commands to extract reusable skills following the
Commands → Skills separation pattern. Each command is now <50 lines
and references skill files for detailed knowledge.

Plugins refactored:
- claude-config-maintainer: 5 commands → 7 skills
- code-sentinel: 3 commands → 2 skills
- contract-validator: 5 commands → 6 skills
- data-platform: 10 commands → 6 skills
- doc-guardian: 5 commands → 6 skills (replaced nested dir)
- git-flow: 8 commands → 7 skills

Skills contain: workflows, validation rules, conventions,
reference data, tool documentation

Commands now contain: YAML frontmatter, agent assignment,
skills list, brief workflow steps, parameters

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/contract-validator/skills/interface-parsing.md

@@ -0,0 +1,52 @@
+# Skill: Interface Parsing
+
+Parse plugin interfaces from README.md and agent definitions from CLAUDE.md.
+
+## Interface Components
+
+| Component | Source | Description |
+|-----------|--------|-------------|
+| Commands | README.md | Slash commands offered by plugin |
+| Agents | README.md, CLAUDE.md | Autonomous agents defined |
+| Tools | README.md | MCP tools provided |
+| Categories | README.md | Tool groupings and features |
+
+## Parsing README.md
+
+Extract from these sections:
+
+1. **Commands section**: Look for tables with `| Command |` or lists of `/command-name`
+2. **Tools section**: Look for tables with `| Tool |` or code blocks with tool names
+3. **Agents section**: Look for "Four-Agent Model" or "Agents" headings
+
+## Parsing CLAUDE.md
+
+Extract agent definitions from:
+
+1. **Four-Agent Model table**: `| Agent | Personality | Responsibilities |`
+2. **Agent sections**: Headings like `### Planner Agent` or `## Agents`
+3. **Tool sequences**: Lists of tools in workflow steps
+
+## Agent Definition Structure
+
+```yaml
+agent:
+  name: "Planner"
+  personality: "Thoughtful, methodical"
+  responsibilities:
+    - "Sprint planning"
+    - "Architecture analysis"
+  tools:
+    - "create_issue"
+    - "search_lessons"
+  workflow:
+    - step: "Analyze requirements"
+      tools: ["list_issues", "get_issue"]
+```
+
+## MCP Tools
+
+| Tool | Purpose |
+|------|---------|
+| `parse_plugin_interface` | Extract interface from README.md |
+| `parse_claude_md_agents` | Extract agents and tool sequences from CLAUDE.md |