Alpha release (1.0.0-alpha)

feat: prepare alpha release (1.0.0-alpha)

- Update README to alpha release version (simplified for merchants)
- Simplify documentation by removing internal sections
- Remove internal documentation files
- Fix recipient and charge ID validation patterns (lowercase-only, 19 chars)
- Add environment configuration templates (.example files)
- Update package.json to 1.0.0-alpha
- Clean repository for merchant-facing release