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>

workplans/CE-WP-0002-pdf-review-slice.md

@@ -64,7 +64,7 @@ T01 (engine types: Document, Representation, Annotation, Selector, EvidenceItem)
 id: CE-WP-0002-T01
 state_hub_task_id: b015c082-4272-407d-b6e4-9e1bd97f0193
 priority: critical
-status: todo
+status: done
 ```
 
 Translate the type definitions in `wiki/SharedContracts.md` §1 and §3 into
@@ -95,7 +95,7 @@ Add JSDoc on each type pointing at the §-reference in
 id: CE-WP-0002-T02
 state_hub_task_id: 59846d9e-7ac1-4306-b02e-0980a52f44c8
 priority: critical
-status: todo
+status: done
 depends_on: [T01]
 ```