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>

.claude/rules/repo-identity.md

@@ -1,4 +1,4 @@
-**Purpose:** Document ingestion, extraction, fingerprinting, citation recovery. Depends only on citation-engine. INTENT-only during umbrella-first MVP.
+**Purpose:** Document ingestion, extraction, fingerprinting, citation recovery. Depends only on citation-engine. The PDF ingest slice is implemented and consumed by citation-evidence (ESRC-WP-0001); HTML/MD, metadata enrichment, and citation recovery are deferred to ESRC-WP-0002..0004.
 
 **Domain:** infotech
 **Repo slug:** evidence-source