feat(contract-validator): create commands (#189)

Add 3 user-facing commands:
- /validate-contracts: Full marketplace compatibility validation
- /check-agent: Validate single agent definition
- /list-interfaces: Show plugin interfaces summary

Each command documents usage, workflow, parameters, and available
MCP tools for implementation.

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

plugins/contract-validator/commands/check-agent.md

@@ -0,0 +1,51 @@
+# /check-agent - Validate Agent Definition
+
+Validate a single agent's tool references and data flow.
+
+## Usage
+
+```
+/check-agent <agent_name> [claude_md_path]
+```
+
+## Parameters
+
+- `agent_name` (required): Name of the agent to validate (e.g., "Planner", "Orchestrator")
+- `claude_md_path` (optional): Path to CLAUDE.md file. Defaults to `./CLAUDE.md`
+
+## Workflow
+
+1. **Parse agent definition**:
+   - Locate agent in CLAUDE.md (Four-Agent Model table or Agents section)
+   - Extract responsibilities, tool references, workflow steps
+
+2. **Validate tool references**:
+   - Check each referenced tool exists in available plugins
+   - Report missing or misspelled tool names
+   - Suggest corrections for common mistakes
+
+3. **Validate data flow**:
+   - Analyze sequence of tools in agent workflow
+   - Verify data producers precede data consumers
+   - Check for orphaned data references
+
+4. **Report findings**:
+   - List all tool references found
+   - List any missing tools
+   - Data flow validation results
+   - Suggestions for improvement
+
+## Examples
+
+```
+/check-agent Planner
+/check-agent Orchestrator ./CLAUDE.md
+/check-agent data-analysis ~/project/CLAUDE.md
+```
+
+## Available Tools
+
+Use these MCP tools:
+- `validate_agent_refs` - Check agent tool references exist
+- `validate_data_flow` - Verify data flow through agent sequence
+- `parse_claude_md_agents` - Parse all agents from CLAUDE.md