Implement CE-WP-0009: wire umbrella to @citation-evidence/engine

Add link: dependency on citation-engine, retarget @shared/@engine aliases,
remove in-repo shared/engine copies. ADR-0002 accepted (option B).
172 tests, typecheck, and lint pass.

vite.config.ts

@@ -31,8 +31,8 @@ export default defineConfig({
   ],
   resolve: {
     alias: {
-      "@shared": resolve(__dirname, "src/shared"),
-      "@engine": resolve(__dirname, "src/engine"),
+      "@shared": resolve(__dirname, "../citation-engine/src/shared"),
+      "@engine": resolve(__dirname, "../citation-engine/src/engine"),
       "@anchor": resolve(__dirname, "src/anchor"),
       "@source": resolve(__dirname, "src/source"),
       "@binder": resolve(__dirname, "src/binder"),
@@ -43,7 +43,7 @@ export default defineConfig({
   server: {
     fs: {
       // Allow Vite to serve /fixtures/pdfs/*.pdf from the project root.
-      allow: [resolve(__dirname)],
+      allow: [resolve(__dirname), resolve(__dirname, "../citation-engine")],
     },
   },
   optimizeDeps: {