Add SVG component support

[Gujiassh]

Adds an initial SVG component implementation for React NodeGui.

What changed:

• Adds a <Svg> host component that serializes SVG-like child components to SVG XML and renders through QPixmap.loadFromData.
• Adds basic SVG nodes: <G>/<Group>, <Rect>, <Circle>, <Ellipse>, <Line>, <Polygon>, and <Path>.
• Exports the new components from the package entrypoint.
• Documents a minimal SVG usage example in the README.

This follows the initial MVP approach discussed in #31: generate an SVG string from React components and render it as an image. Prop updates regenerate the SVG image.

Validation:

• ./node_modules/.bin/tsc --noEmit --pretty false
• git diff --check

Note: yarn install --frozen-lockfile could not complete the @nodegui/nodegui Qt download in this environment due a TLS ECONNRESET, but the TypeScript dependencies were present and static validation passed.

/claim #31