- parse the Basic auth-scheme case-insensitively (RFC 7235), matching Bearer
- register the http_server test only when pip_http_server and pip_http_client
targets exist, so TESTS=ON without the HTTP modules does not fail to link
- add a Basic_LowercaseScheme test
- PIHTTPServerBasicAuth: parse Authorization: Basic header, validate credentials via callback
- PIHTTPServerProtected: wrap any handler with auth check (basic or custom token)
- Integration tests for both modules (12 test cases)