EANCH-WP-0001 T02: bootstrap standalone TS package + test harness

Add package.json (name evidence-anchor, exports . and ./pdf, scripts
test/typecheck/lint), tsconfig.json (mirrors engine, DOM+jsx), vitest.config.ts
(happy-dom + react plugin), eslint.config.js (confines viewer libs to src/pdf/),
.nvmrc, and placeholder src entrypoints. Depends on @citation-evidence/engine
via sibling-checkout link only; no citation-evidence internals.

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

src/index.ts

@@ -0,0 +1,10 @@
+// Public entrypoint for `evidence-anchor`.
+//
+// The stable surface consumers depend on is re-exported from here:
+//   - selector creation/resolution:  ./selectors  (T03)
+//   - adapter-side types + contract: ./types      (T03)
+//   - the concrete PDF adapter:      ./pdf         (T04, also exposed at `evidence-anchor/pdf`)
+//
+// Populated during the extraction tasks; kept as an explicit placeholder so the
+// package resolves and typechecks before the code lands.
+export {};

src/pdf/index.ts

@@ -0,0 +1,6 @@
+// Subpath entrypoint `evidence-anchor/pdf` — the concrete PDF viewer adapter and
+// its helpers. Keeping the adapter behind a subpath lets pure consumers use the
+// selector/resolution core without pulling PDF.js or React into their bundle.
+//
+// Populated in T04 (PDF adapter extraction); explicit placeholder for now.
+export {};