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

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+# /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

plugins/contract-validator/commands/list-interfaces.md

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+# /list-interfaces - Show Plugin Interfaces
+
+Display what each plugin in the marketplace produces and accepts.
+
+## Usage
+
+```
+/list-interfaces [marketplace_path]
+```
+
+## Parameters
+
+- `marketplace_path` (optional): Path to marketplace root. Defaults to current project root.
+
+## Workflow
+
+1. **Discover plugins**:
+   - Scan plugins directory for all plugins with `.claude-plugin/` marker
+   - Read each plugin's README.md
+
+2. **Parse interfaces**:
+   - Extract commands (slash commands offered by plugin)
+   - Extract agents (autonomous agents defined)
+   - Extract tools (MCP tools provided)
+   - Identify tool categories and features
+
+3. **Display summary**:
+   - Table of plugins with command/agent/tool counts
+   - Detailed breakdown per plugin
+   - Tool categories and their contents
+
+## Output Format
+
+```
+| Plugin      | Commands | Agents | Tools |
+|-------------|----------|--------|-------|
+| projman     | 12       | 4      | 26    |
+| data-platform| 7       | 2      | 32    |
+| ...         | ...      | ...    | ...   |
+
+## projman
+- Commands: /sprint-plan, /sprint-start, ...
+- Agents: Planner, Orchestrator, Executor, Code Reviewer
+- Tools: list_issues, create_issue, ...
+```
+
+## Examples
+
+```
+/list-interfaces
+/list-interfaces ~/claude-plugins-work
+```
+
+## Available Tools
+
+Use these MCP tools:
+- `parse_plugin_interface` - Parse individual plugin README
+- `generate_compatibility_report` - Get full interface data (JSON format)

plugins/contract-validator/commands/validate-contracts.md

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+# /validate-contracts - Full Contract Validation
+
+Run comprehensive cross-plugin compatibility validation for the entire marketplace.
+
+## Usage
+
+```
+/validate-contracts [marketplace_path]
+```
+
+## Parameters
+
+- `marketplace_path` (optional): Path to marketplace root. Defaults to current project root.
+
+## Workflow
+
+1. **Discover plugins**:
+   - Scan plugins directory for all plugins with `.claude-plugin/` marker
+   - Parse each plugin's README.md to extract interface
+
+2. **Run compatibility checks**:
+   - Perform pairwise compatibility validation between all plugins
+   - Check for command name conflicts
+   - Check for tool name overlaps
+   - Identify interface mismatches
+
+3. **Validate CLAUDE.md agents**:
+   - Parse agent definitions from CLAUDE.md
+   - Validate all tool references exist
+   - Check data flow through agent sequences
+
+4. **Generate report**:
+   - Summary statistics (plugins, commands, tools, issues)
+   - Detailed findings by severity (error, warning, info)
+   - Actionable suggestions for each issue
+
+## Examples
+
+```
+/validate-contracts
+/validate-contracts ~/claude-plugins-work
+```
+
+## Available Tools
+
+Use these MCP tools:
+- `generate_compatibility_report` - Generate full marketplace report
+- `list_issues` - Filter issues by severity or type
+- `parse_plugin_interface` - Parse individual plugin interface
+- `validate_compatibility` - Check two plugins for conflicts