Bump version to 0.5.2 and update changelog

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

CHANGELOG.md

@@ -7,6 +7,27 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.5.2] - 2026-01-26
+
+### Added
+
+- Per-license customer secrets for API response verification
+- "API Verification Secret" section in customer account licenses page (collapsible)
+- Copy button for customer secrets with clipboard support
+- Documentation for per-license secret derivation and usage
+
+### Security
+
+- Customers no longer need the master server secret for signature verification
+- Each license key has a unique derived secret using HKDF-like key derivation
+- If one customer's secret is compromised, other customers remain unaffected
+
+### Changed
+
+- Updated `ResponseSigner` with static methods for secret derivation
+- Updated `server-implementation.md` with per-license secret documentation
+- Added new translation strings for secret-related UI
+
 ## [0.5.1] - 2026-01-26
 
 ### Fixed