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/annotation.ts

@@ -0,0 +1,45 @@
+/**
+ * The Annotation type.
+ *
+ * Implements `wiki/SharedContracts.md` §1 (vocabulary), §2.1 (resolutionStatus)
+ * and `wiki/ArchitectureOverview.md` §4.4. Annotations are the *technical*
+ * mark on a document range — meaning and commentary live on EvidenceItem.
+ */
+
+import type { AnnotationId, DocumentId, RepresentationId } from "./ids";
+import type { Selector } from "./selector";
+
+/** Closed enum per `wiki/SharedContracts.md` §2.1. */
+export type AnnotationResolutionStatus =
+  | "resolved"
+  | "ambiguous"
+  | "unresolved"
+  | "stale";
+
+export interface Annotation {
+  readonly id: AnnotationId;
+  readonly documentId: DocumentId;
+  readonly representationId?: RepresentationId;
+  /**
+   * All available selectors for this passage, in order of expected
+   * resolution confidence. Per the §3 redundancy rule, the system stores
+   * every selector kind it could derive at capture time.
+   */
+  readonly selectors: readonly Selector[];
+  /** Verbatim canonical text at capture time. */
+  readonly quote?: string;
+  /** Short human note attached to the technical mark. */
+  readonly note?: string;
+  /**
+   * Version of `normalize()` that was active when these selectors were
+   * stored. Recorded so future normalization changes can be detected as a
+   * migration concern. See `src/shared/text/normalize.ts`.
+   */
+  readonly normalizeVersion: number;
+  readonly resolutionStatus?: AnnotationResolutionStatus;
+  readonly createdBy?: string;
+  /** ISO-8601 timestamp. */
+  readonly createdAt: string;
+  /** ISO-8601 timestamp. */
+  readonly updatedAt: string;
+}