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>

src/shared/ids.test.ts

@@ -0,0 +1,21 @@
+import { describe, it, expect } from "vitest";
+import { newId } from "./ids";
+
+describe("newId", () => {
+  it("returns ids with the expected prefix for each kind", () => {
+    expect(newId("document")).toMatch(/^doc_[0-9a-f-]{36}$/);
+    expect(newId("representation")).toMatch(/^rep_[0-9a-f-]{36}$/);
+    expect(newId("annotation")).toMatch(/^ann_[0-9a-f-]{36}$/);
+    expect(newId("evidence")).toMatch(/^ev_[0-9a-f-]{36}$/);
+    expect(newId("evidence-set")).toMatch(/^evset_[0-9a-f-]{36}$/);
+    expect(newId("evidence-link")).toMatch(/^evlink_[0-9a-f-]{36}$/);
+    expect(newId("citation-card")).toMatch(/^card_[0-9a-f-]{36}$/);
+    expect(newId("citation-recovery")).toMatch(/^crec_[0-9a-f-]{36}$/);
+  });
+
+  it("returns a unique id on every call", () => {
+    const a = newId("annotation");
+    const b = newId("annotation");
+    expect(a).not.toBe(b);
+  });
+});