Add comprehensive client implementation documentation

- Create docs/client-implementation.md with full integration guide
- Document all classes: clients, DTOs, exceptions, security classes
- Add integration examples for WordPress, Laravel, Symfony
- Include best practices and troubleshooting sections
- Update README with documentation links

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

CLAUDE.md

@@ -29,6 +29,14 @@ This project is proudly **"vibe-coded"** using Claude.AI - the entire codebase w
 
 No known bugs at the moment
 
+### Version 0.1.1
+
+No changes at the moment.
+
+### Version 0.2.0
+
+No changes at the moment.
+
 ## Technical Stack
 
 - **Language:** PHP 8.3.x
@@ -153,3 +161,23 @@ When editing CLAUDE.md or other markdown files, follow these rules to avoid lint
 - StringEncoder uses XOR with expanded key for simple obfuscation (not encryption)
 - PHPUnit 11 uses PHP 8 attributes (`#[Test]`, `#[CoversClass]`) instead of annotations
 - OpenAPI spec (tmp/openapi.json) updated to v0.3.2 with signature header definitions
+
+### 2026-01-23 - Client Documentation
+
+**Completed:**
+
+- Created comprehensive `docs/client-implementation.md` documentation
+- Documented all classes: LicenseClient, SecureLicenseClient, DTOs, Exceptions, Security classes
+- Added integration guides for: Basic PHP, WordPress plugins, Laravel, Symfony
+- Documented constructor parameters, method signatures, and return types
+- Added complete exception hierarchy reference with error codes
+- Included best practices section for production use
+- Added API reference with endpoints and request/response formats
+- Added troubleshooting section for common issues
+- Updated README.md with documentation links section
+
+**Learnings:**
+
+- Client documentation complements server documentation for complete integration guide
+- Integration examples for major PHP frameworks help adoption
+- Error code mapping to exception classes aids programmatic error handling