Add drag-and-drop upload component with chunked uploads and offline support

CHANGELOG.md

@@ -7,6 +7,41 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Added
+- Added reusable `DragDropUpload` component for artifact uploads (#8)
+  - Drag-and-drop file selection with visual feedback
+  - Click-to-browse fallback
+  - Multiple file upload support with queue management
+  - Real-time progress indicators with speed and ETA
+  - File type and size validation (configurable)
+  - Concurrent upload handling (configurable max concurrent)
+  - Automatic retry with exponential backoff for network errors
+  - Individual file status (pending, uploading, complete, failed)
+  - Retry and remove actions per file
+  - Auto-dismiss success messages after 5 seconds
+- Integrated DragDropUpload into PackagePage replacing basic file input (#8)
+- Added frontend testing infrastructure with Vitest and React Testing Library (#14)
+  - Configured Vitest for React/TypeScript with jsdom
+  - Added 24 unit tests for DragDropUpload component
+  - Tests cover: rendering, drag-drop events, file validation, upload queue, progress, errors
+- Added chunked upload support for large files (#9)
+  - Files >100MB automatically use chunked upload API (10MB chunks)
+  - Client-side SHA256 hash computation via Web Crypto API
+  - localStorage persistence for resume after browser close
+  - Deduplication check at upload init phase
+- Added offline detection and network resilience (#12)
+  - Automatic pause when browser goes offline
+  - Auto-resume when connection restored
+  - Offline banner UI with status message
+  - XHR abort on network loss to prevent hung requests
+- Added download by artifact ID feature (#10)
+  - Direct artifact ID input field on package page
+  - Hex-only input validation with character count
+  - File size and filename displayed in tag list
+- Added backend security tests (#15)
+  - Path traversal prevention tests for upload/download
+  - Malformed request handling tests
+  - Checksum validation tests
+  - 10 new security-focused integration tests
 - Added download verification with `verify` and `verify_mode` query parameters (#26)
   - `?verify=true&verify_mode=pre` - Pre-verification: verify before streaming (guaranteed no corrupt data)
   - `?verify=true&verify_mode=stream` - Streaming verification: verify while streaming (logs error if mismatch)