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>

package.json

@@ -11,7 +11,7 @@
   },
   "scripts": {
     "dev": "vite",
-    "build": "tsc -b && vite build",
+    "build": "tsc -b --noEmit && vite build",
     "preview": "vite preview",
     "test": "vitest run",
     "test:watch": "vitest",
@@ -19,8 +19,10 @@
     "typecheck": "tsc -b --noEmit"
   },
   "dependencies": {
+    "pdfjs-dist": "^4.4.168",
     "react": "^18.3.1",
-    "react-dom": "^18.3.1"
+    "react-dom": "^18.3.1",
+    "react-pdf-highlighter-plus": "^1.1.4"
   },
   "devDependencies": {
     "@types/node": "^20.14.0",