EANCH-WP-0001 T03: extract pure selector creation + resolution core

Move types.ts, selectors/{index,create,resolve}.ts, and pdf-selector-math.ts
out of citation-evidence/src/anchor/ into src/ (pdf math under src/pdf/).
Rewrite all @shared/* imports to @citation-evidence/engine/shared; wire the
public entrypoint (src/index.ts) and the ./pdf subpath. Port the three unit
suites. Confidence ladder and selector-redundancy rules preserved verbatim.

Verified: pnpm test (29 passed), typecheck, and lint all green.
Also adds Node/TS .gitignore entries and the pnpm lockfile.

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

src/index.ts

@@ -1,10 +1,16 @@
 // 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`)
+// The stable surface consumers depend on:
+//   - adapter-side types + the viewer contract  (./types)
+//   - selector creation / resolution             (./selectors)
 //
-// Populated during the extraction tasks; kept as an explicit placeholder so the
-// package resolves and typechecks before the code lands.
-export {};
+// The concrete PDF adapter lives behind the `evidence-anchor/pdf` subpath
+// (./pdf) so pure consumers do not pull PDF.js or React into their bundle.
+
+export * from "./types";
+export {
+  createSelectors,
+  resolveSelectors,
+  DEFAULT_CONTEXT_CHARS,
+  type CreateSelectorsOptions,
+} from "./selectors";