Address final review feedback and commit production assets

[Copilot]

Final review pass to address remaining code review comments and prepare the plugin for distribution.

Code Quality Improvements

• Version detector: Removed advertised capabilities without implementation (post_format_suggestion, validate_proxy_url, validate_request_ip, press_this_data)
• Timeout management: Refactored to use useRef instead of state, ensuring cleanup on unmount prevents memory leaks
• REST validation: Added null check for request body to prevent warnings on malformed requests
• Dependency cleanup: Removed unused @wordpress packages (block-editor, data, icons)
• Nonce middleware: Added validation before registration to prevent failures when localized data is missing
• Experimental API: Replaced __experimentalText with stable <span> element for cross-version compatibility

Production Assets

Built and committed React settings UI to build/ directory. The plugin now ships with compiled assets instead of requiring end users to run the build process.

// Before: timeout could leak on unmount
const [timeoutId, setTimeoutId] = useState(null);
setTimeout(() => setSaved(false), 3000);

// After: guaranteed cleanup
const timeoutRef = useRef(null);
useEffect(() => () => clearTimeout(timeoutRef.current), []);
timeoutRef.current = setTimeout(() => setSaved(false), 3000);

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