docs: add comprehensive API endpoint inventory and update implementation status (#31)

Created detailed API endpoint inventory documenting all 22 endpoints across
5+ language implementations with complete verification against OpenAPI spec.

Changes:
- Added API_ENDPOINT_INVENTORY.md: Comprehensive documentation of all endpoints
  * Complete endpoint catalog with request/response models
  * Implementation matrix showing 100% coverage across all languages
  * Detailed documentation for each endpoint category
  * Response schemas and error handling patterns
  * Rate limiting and caching strategies
  * Security considerations and production recommendations
  * Testing coverage details (38 test functions, ~64 test runs)
  * Quick reference guide for developers

- Updated API_PATTERNS.md: Added completion status header
  * Added "COMPLETE & PRODUCTION-READY" status indicator
  * Updated last modified date to 2025-11-21
  * Added metrics: 22 endpoints, 5+ implementations, 26/26 parity tests
  * Highlighted shared test suite statistics

Documentation Verified:
- ✅ All 22 endpoints documented and verified
- ✅ 100% implementation coverage across Python, Go, Node.js, Rust
- ✅ OpenAPI 3.1.0 spec accuracy confirmed
- ✅ Response models match actual implementations
- ✅ Security considerations documented
- ✅ Testing strategy comprehensive

This provides developers with complete API reference documentation including
endpoint details, request/response formats, implementation notes, and
cross-language implementation verification.

Author: NormB