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>

docs/ADR-0002-fixture-ownership.md

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+# ADR-0002 — Fixture corpus ownership
+
+- **Status:** accepted
+- **Date:** 2026-07-08
+- **Workplan:** ESRC-WP-0001 (T05)
+
+## Context
+
+The PDF ingest contract tests are driven by a fixture corpus
+(`fixtures/pdfs/` + `manifest.json`) currently owned by `citation-evidence`.
+The corpus is made of **real** personal and legal documents — utility-cost
+statements, a settlement letter, court correspondence, cemetery admission
+forms — containing names, addresses, and case details.
+
+The workplan (T05) asks us to either copy the corpus into this repo or define a
+stable shared-fixture path.
+
+## Decision
+
+Do **not** copy the corpus into `evidence-source`. Resolve it from the sibling
+`citation-evidence` checkout instead:
+
+- default: `<repo>/../citation-evidence/fixtures/pdfs`
+- override: `EVIDENCE_SOURCE_FIXTURE_DIR` environment variable
+
+## Rationale
+
+- **Privacy.** `evidence-source` advertises reusable ingest capability and is a
+  candidate for wider distribution. Duplicating real PII into it multiplies the
+  places that data lives and can be leaked.
+- **Single ownership.** The corpus and its `manifest.json` (page counts,
+  known-good quotes) were curated and re-verified upstream. One owner avoids
+  drift between two copies.
+- **Consistent coupling.** This repo already assumes a sibling checkout for its
+  `@citation-evidence/engine` (`link:../citation-engine`) dependency. Reading
+  fixtures from `../citation-evidence` is the same coupling model, not a new one.
+
+## Consequences
+
+- Tests require a sibling `citation-evidence` checkout. In CI or a standalone
+  clone, point `EVIDENCE_SOURCE_FIXTURE_DIR` at wherever the corpus is mounted.
+- When the corpus is absent, the fixture-driven suites skip with a clear message
+  rather than failing spuriously, so unit tests that need no corpus still run.