Implement CE-WP-0002 T01-T02: engine types + PDF viewer adapter spike

T01: shared engine types (Document, Selector union, Annotation, EvidenceItem,
branded IDs with newId factory) per wiki/SharedContracts.md §1-§3.

T02: react-pdf-highlighter-plus v1.1.4 spike behind the §5
DocumentViewerAdapter contract in src/anchor/. Pure round-trip math
extracted to pdf-selector-math.ts with 11 unit tests proving lossless
capture → selectors → JSON → restored-rects. ADR-0004 accepted; full
user-flow Playwright verification deferred to T09.

Adds Vite app shell (index.html, src/app/SpikeApp.tsx) so the spike is
exercisable via pnpm dev. tsconfig --noEmit prevents tsc -b from
littering src/ with stray .js outputs.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

vite.config.ts

@@ -0,0 +1,31 @@
+import { defineConfig } from "vite";
+import react from "@vitejs/plugin-react";
+import { fileURLToPath } from "node:url";
+import { dirname, resolve } from "node:path";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+export default defineConfig({
+  plugins: [react()],
+  resolve: {
+    alias: {
+      "@shared": resolve(__dirname, "src/shared"),
+      "@engine": resolve(__dirname, "src/engine"),
+      "@anchor": resolve(__dirname, "src/anchor"),
+      "@source": resolve(__dirname, "src/source"),
+      "@binder": resolve(__dirname, "src/binder"),
+      "@work":   resolve(__dirname, "src/work"),
+      "@app":    resolve(__dirname, "src/app"),
+    },
+  },
+  server: {
+    fs: {
+      // Allow Vite to serve /fixtures/pdfs/*.pdf from the project root.
+      allow: [resolve(__dirname)],
+    },
+  },
+  optimizeDeps: {
+    // pdfjs-dist ships its worker as a .mjs Vite needs to handle.
+    exclude: ["pdfjs-dist"],
+  },
+});