feat(pdf): extract standalone PDF ingest package (ESRC-WP-0001)

Bootstrap evidence-source from the citation-evidence src/source PDF slice.

- Headless core (src/pdf): ingest/extract/fingerprint, importing domain
  contracts from @citation-evidence/engine/shared (no local copies)
- Browser upload helpers isolated under src/browser behind a ./browser
  entry point, with an eslint boundary keeping the core browser-free
- pnpm/TS/vitest/eslint scaffold; 52 tests (contract + determinism)
- Fixtures resolved from the sibling citation-evidence checkout, not
  duplicated (real PII) — see docs/ADR-0002; suites skip when absent
- Boundary + fixture decisions recorded as docs/ADR-0001 / ADR-0002
- README/SCOPE rewritten; capability.infotech.pdf-evidence-ingest
  registered, NO_CAPABILITIES removed
- Follow-on workplans ESRC-WP-0002..0004 queued; ESRC-WP-0001 finished

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

tests/setup-pdf-worker.ts

@@ -0,0 +1,17 @@
+/**
+ * Vitest setup: point PDF.js at its legacy worker bundle for Node runs.
+ *
+ * `extractPdf` deliberately does no worker setup (so the same module loads in
+ * browsers and Node). In Node tests we configure `GlobalWorkerOptions.workerSrc`
+ * here, once per test file, before any extraction runs. The legacy bundle ships
+ * as plain JS and works through PDF.js's fake-worker fallback when no real
+ * Worker is available.
+ */
+
+import { createRequire } from "node:module";
+import * as pdfjs from "pdfjs-dist";
+
+const require = createRequire(import.meta.url);
+pdfjs.GlobalWorkerOptions.workerSrc = require.resolve(
+  "pdfjs-dist/legacy/build/pdf.worker.mjs",
+);