refactor(anchor): consume extracted evidence-anchor package (EANCH-WP-0001-T05)

Replace the in-repo src/anchor/ slice with a dependency on the extracted
@citation-evidence/evidence-anchor package (link:../evidence-anchor).

- package.json: add the link dependency
- repoint all @anchor/{index,selectors,types} imports and vi.mock targets to
  the package barrel; the node-env anchor-source-roundtrip test uses the pure
  ./selectors and ./types subpaths (no pdfjs pulled into a node environment)
- drop the @anchor alias from tsconfig paths and vite resolve
- delete src/anchor/ (behavior now owned by evidence-anchor)

Verified green: pnpm typecheck, pnpm test (26 files / 95 tests), pnpm build.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/integration/forms-field-values.dom.test.tsx

@@ -10,8 +10,8 @@ import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
 import manifest from "../../fixtures/pdfs/manifest.json" with { type: "json" };
 
-vi.mock("@anchor/index", async (importOriginal) => {
-  const original = await importOriginal<typeof import("@anchor/index")>();
+vi.mock("@citation-evidence/evidence-anchor", async (importOriginal) => {
+  const original = await importOriginal<typeof import("@citation-evidence/evidence-anchor")>();
   const MockPdfSpikeViewer = () => (
     <div data-testid="mock-pdf-viewer" />
   );