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>

workplans/ESRC-WP-0003-metadata-enrichment.md

@@ -0,0 +1,48 @@
+---
+id: ESRC-WP-0003
+type: workplan
+title: "Document metadata enrichment beyond pass-through options"
+domain: infotech
+repo: evidence-source
+status: proposed
+owner: codex
+topic_slug: citation_evidence_mvp
+created: "2026-07-08"
+updated: "2026-07-08"
+spec_refs:
+  - README.md
+  - src/pdf/ingest.ts
+---
+
+# ESRC-WP-0003 — Metadata enrichment
+
+Today `ingestPdf` only passes through caller-supplied `title`/`uri`/`metadata`.
+This workplan extracts intrinsic document metadata (PDF info dictionary,
+embedded XMP, page-derived signals like author/creation date/title) and folds
+it into the `Document` record without breaking the pure-over-bytes contract.
+
+## Sketch
+
+```task
+id: ESRC-WP-0003-T01
+status: todo
+priority: low
+```
+Enumerate available PDF metadata sources (info dict, XMP) via PDF.js and decide
+precedence vs. caller-supplied options (caller wins).
+
+```task
+id: ESRC-WP-0003-T02
+status: todo
+priority: low
+```
+Implement extraction into a normalized metadata shape; keep it optional so
+minimal-metadata PDFs still ingest cleanly.
+
+```task
+id: ESRC-WP-0003-T03
+status: todo
+priority: low
+```
+Contract tests over the fixture corpus asserting extracted vs. overridden
+metadata precedence.