v0.3.0 of mcp_playground_flutter

Interactive AI Agent Playground widget for Flutter. Connect to any LLM provider, register Dart-native tools, remote HTTP MCP servers, and local Node.js or Python subprocesses. Changelog excerpt: - **Architecture modularization**: Extracted reusable Flutter UI components, dialogs, drawers, and state controllers into the [`mcp_playground_ui`](../mcp_playground_ui)shared package. - **Standalone GenUI separation**: Moved GenUI generative UI surfaces, catalog builders, and controllers into the dedicated [`genui_mcp_playground`](../genui_mcp_playground)package. - **Agent Inspector Toggle**: Added `showAgentInspector`parameter (defaults to `true`) and top AppBar toggle button to control Agent [...]