Extract engine from citation-evidence umbrella (CENG-WP-0001)

Bootstrap @citation-evidence/engine as a standalone TypeScript package
with shared types and engine services copied from the umbrella MVP.
All 89 tests pass with lint and typecheck clean.

vitest.config.ts

@@ -0,0 +1,18 @@
+import { defineConfig } from "vitest/config";
+import { dirname, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+export default defineConfig({
+  resolve: {
+    alias: {
+      "@shared": resolve(__dirname, "src/shared"),
+      "@engine": resolve(__dirname, "src/engine"),
+    },
+  },
+  test: {
+    environment: "node",
+    globals: false,
+  },
+});