Fix Anki integration to support non-English environments and custom models

Problem The extension only worked with English Anki installations using the "Basic" model with "Front"/"Back" fields, failing for users with: - Non-English Anki (Chinese, Japanese, etc.) - Custom note types - Different field names Solution - Auto-detect compatible models: Scans all available note types and tests compatibility by creating/deleting test cards - Language-agnostic: Works with any field names in any language - Smart fallback: Prefers Front/Back fields but falls back to first two fields of any model - Better error handling: Clear error messages when no compatible model is found Changes - Added findCompatibleModel() to automatically discover usable note types - Added testModelCompatibility() to verify models work before use - Removed hardcoded "Basic" model and "Front"/"Back" field names - Added duplicate prevention with allowDuplicate: false Testing Tested with: - ✅ English Anki (Basic model) - ✅ Chinese Anki (基础 model) Fixes #272