Fix CORS headers for AWS SDK v3 compatibility

- Use wildcard (*) for Access-Control-Allow-Headers and Access-Control-Expose-Headers
- Add comprehensive CORS integration tests
- Improve test coverage to 86.3%
- Add CHANGELOG.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: pierre-b

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [v1.1] - 2025-11-28
+
+### Fixed
+- CORS headers now use wildcards (`*`) for `Access-Control-Allow-Headers` and `Access-Control-Expose-Headers` to support AWS SDK v3 and other S3 clients that send custom headers like `amz-sdk-invocation-id` and `amz-sdk-request`
+
+### Added
+- Comprehensive CORS integration tests covering:
+  - Preflight (OPTIONS) requests
+  - Simple GET/HEAD requests with Origin header
+  - Wildcard origin support
+  - Error response CORS headers
+  - S3-specific header handling
+  - DELETE preflight requests
+  - Max-age caching verification
+
+### Improved
+- Test coverage increased to 86.3% overall
+  - Server: 85.3%
+  - Storage: 77.1%
+  - Auth: 93.7%
+  - Config: 100%
+
+## [v1.0] - 2025-11-28
+
+### Added
+- Initial release of SelfhostS3
+- S3-compatible object storage server
+- AWS Signature V4 authentication
+- Public file access with configurable prefix (default: `public/`)
+- Cache-Control headers for public files
+- Download parameter (`?download=1`) for Content-Disposition header
+- CORS support with configurable origins
+- Health check endpoint (`/health`)
+- Docker support with multi-platform builds (amd64, arm64)
+- GitHub Actions CI/CD workflows
+- Comprehensive unit and integration tests
+
+### Features
+- **Storage Operations**: PUT, GET, HEAD, DELETE objects
+- **Listing**: ListObjectsV2 with prefix filtering
+- **Content Types**: Automatic MIME type detection from file extension
+- **Security**: Path traversal protection, AWS Sig V4 authentication
+- **Public Access**: Unauthenticated GET/HEAD for public prefix
+- **Configuration**: Environment variable based configuration

codecov.yml

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+coverage:
+  status:
+    project:
+      default:
+        target: 70%
+        threshold: 10%
+    patch: off
+  range: '60...80'
+  # Exclude mock files from coverage calculation
+  ignore:
+    - '**/cmd/**'
+    - '**/integration/**'