docs: update documentation for contract-validator (Sprint 2)

- CHANGELOG.md: Add Sprint 2 completion notes in [Unreleased]
- README.md: Add contract-validator plugin section
- docs/CANONICAL-PATHS.md: Add contract-validator paths
- docs/COMMANDS-CHEATSHEET.md: Add contract-validator commands

Preparing for v5.0.0 release.

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

CHANGELOG.md

@@ -8,6 +8,32 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
+#### Sprint 2: contract-validator Plugin ✅ Completed
+- **contract-validator** v1.0.0 - Cross-plugin compatibility validation and CLAUDE.md agent verification
+  - **Parse Tools** (2 tools): `parse_plugin_interface`, `parse_claude_md_agents`
+    - Extracts commands, agents, tools from plugin README.md files
+    - Parses CLAUDE.md Four-Agent Model tables and Agents sections
+  - **Validation Tools** (3 tools): `validate_compatibility`, `validate_agent_refs`, `validate_data_flow`
+    - Pairwise plugin compatibility checks for command/tool conflicts
+    - Agent tool reference validation against available plugins
+    - Data flow validation for producer/consumer sequences
+  - **Report Tools** (2 tools): `generate_compatibility_report`, `list_issues`
+    - Full marketplace validation reports (markdown or JSON)
+    - Filtered issue listing by severity or type
+  - **Commands**: `/validate-contracts`, `/check-agent`, `/list-interfaces`
+  - **Agents**: `full-validation`, `agent-check`
+  - **Tests**: 34 tests passing
+    - parse_tools.py: 79% coverage
+    - validation_tools.py: 96% coverage
+    - report_tools.py: 89% coverage
+
+**Sprint Completed:**
+- Milestone: Sprint 2 - contract-validator Plugin (closed 2026-01-26)
+- Issues: #185-#193 (9/9 closed)
+- Real issue discovered: `/initial-setup` command conflict between projman, data-platform, and pr-review
+
+---
+
 #### Sprint 1: viz-platform Plugin ✅ Completed
 - **viz-platform** v1.0.0 - Visualization tools with Dash Mantine Components validation and theming
   - **DMC Tools** (3 tools): `list_components`, `get_component_props`, `validate_component`