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.ts

@@ -0,0 +1,55 @@
+/**
+ * Branded ID types and the `newId(kind)` factory.
+ *
+ * Implements the identifier portion of `wiki/SharedContracts.md` §1 and
+ * `wiki/ArchitectureOverview.md` §3.2. Each branded type is structurally a
+ * `string` but nominally distinct, so passing an `AnnotationId` where a
+ * `DocumentId` is required is a compile-time error.
+ */
+
+declare const __brand: unique symbol;
+
+type Brand<K, T extends string> = K & { readonly [__brand]: T };
+
+export type DocumentId = Brand<string, "DocumentId">;
+export type RepresentationId = Brand<string, "RepresentationId">;
+export type AnnotationId = Brand<string, "AnnotationId">;
+export type EvidenceItemId = Brand<string, "EvidenceItemId">;
+export type EvidenceSetId = Brand<string, "EvidenceSetId">;
+export type EvidenceLinkId = Brand<string, "EvidenceLinkId">;
+export type CitationCardId = Brand<string, "CitationCardId">;
+export type CitationRecoveryAttemptId = Brand<string, "CitationRecoveryAttemptId">;
+
+export type IdKindMap = {
+  document: DocumentId;
+  representation: RepresentationId;
+  annotation: AnnotationId;
+  evidence: EvidenceItemId;
+  "evidence-set": EvidenceSetId;
+  "evidence-link": EvidenceLinkId;
+  "citation-card": CitationCardId;
+  "citation-recovery": CitationRecoveryAttemptId;
+};
+
+export type IdKind = keyof IdKindMap;
+
+const PREFIXES: Record<IdKind, string> = {
+  document: "doc",
+  representation: "rep",
+  annotation: "ann",
+  evidence: "ev",
+  "evidence-set": "evset",
+  "evidence-link": "evlink",
+  "citation-card": "card",
+  "citation-recovery": "crec",
+};
+
+/**
+ * Mint a new branded identifier of the requested kind.
+ *
+ * IDs use the shape `<prefix>_<uuid>` so they are human-recognizable when
+ * they show up in logs, URLs, or stored JSON.
+ */
+export function newId<K extends IdKind>(kind: K): IdKindMap[K] {
+  return `${PREFIXES[kind]}_${crypto.randomUUID()}` as IdKindMap[K];
+}