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>

vitest.config.ts

@@ -0,0 +1,14 @@
+import { defineConfig } from "vitest/config";
+
+// Headless-only test surface: every test runs in Node, which has full
+// pdfjs-dist legacy-worker support. There is no DOM/React surface in this
+// repo, so unlike the umbrella app we do not register a happy-dom
+// environment. The browser upload helpers (`src/browser/`) are exercised
+// with injected URL stubs, so they run in Node too.
+export default defineConfig({
+  test: {
+    globals: false,
+    include: ["src/**/*.test.ts", "tests/**/*.test.ts"],
+    setupFiles: ["tests/setup-pdf-worker.ts"],
+  },
+});