Adds a backup check that validates the response body starts with '{'
before attempting JSON unmarshal. This catches cases where:
- Server returns HTML with incorrect Content-Type header
- Reverse proxy/load balancer modifies headers but not body
- PHP error pages with HTTP 200 status
Includes a preview of the HTML content (up to 200 chars) for debugging.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add core JSON-RPC 2.0 protocol implementation for Kanboard API:
- JSONRPCRequest/Response/Error structs with proper JSON tags
- Generic call() method for sending requests and parsing responses
- Thread-safe request ID generation using atomic.Int64
- Automatic /jsonrpc.php path appending to baseURL
- Support for subdirectory installations
- HTTP Basic Auth support (API token and username/password)
- Error handling for unauthorized/forbidden responses
Includes comprehensive tests with httptest mock server.
Closes: kanboard-api-2g1
