fix: replace import.meta.resolve with direct path in mermaid test

import.meta.resolve is not supported in Vitest's module runner,
causing CI to fail. Use a direct node_modules path to locate the
astro-mermaid integration entry point instead.

Author: cursoragent

tests/mermaid-rendering.test.ts

@@ -128,7 +128,12 @@ describe("Mermaid Rendering Validation", () => {
       // Verify the integration source contains the view transitions handler.
       // This is the key fix: the handler must be registered unconditionally
       // so that navigating from a page without diagrams to one with them works.
-      const entrypoint = fileURLToPath(import.meta.resolve("astro-mermaid"));
+      const entrypoint = join(
+        ROOT,
+        "node_modules",
+        "astro-mermaid",
+        "astro-mermaid-integration.js",
+      );
       const content = readFileSync(entrypoint, "utf-8");
       expect(content).toContain("astro:after-swap");
     });