fix(mcp): handle links inside SVG in the document bridge

[asasemahmed]

The click handler in the assemble_document bridge calls a.href.startsWith(...). On an SVG <a>, href is an SVGAnimatedString, not a string. So clicking a link inside a generated SVG diagram:

• throws a.href.startsWith is not a function,
• posts no open-link message,
• skips preventDefault(), so the iframe navigates itself to the target.

The handler now reads href.baseVal, resolved against document.baseURI, when href is not a string. HTML links behave as before.

Tests: tests/renderer.test.ts runs the bridge script against small stubs and checks that both an HTML anchor and an SVG anchor post open-link and prevent the default navigation.