feat: Phase 0 workspace, spikes, and golden harness

Stand up the monorepo skeleton and land the first Phase 0 artifacts:
pairing threat model, plugin catalog, builder detect, 20-prompt golden
harness, and synthetic 2GB mirror timing.

e2e/golden/src/check-assertion.ts

@@ -0,0 +1,20 @@
+import type { GoldenAssert, SiteFixture } from './types.ts';
+
+export type AssertionResult = {
+  ok: boolean;
+};
+
+function pageText(site: SiteFixture, slug: string): string {
+  const post = site.posts.find((item) => item.slug === slug);
+  if (post === undefined) {
+    return '';
+  }
+  return `${post.content}\n${Object.values(post.meta).join('\n')}`;
+}
+
+export function checkAssertion(site: SiteFixture, assertion: GoldenAssert): AssertionResult {
+  if (assertion.type === 'option') {
+    return { ok: site.options[assertion.key] === assertion.value };
+  }
+  return { ok: pageText(site, assertion.page).includes(assertion.contains) };
+}