docs: document policy OCR capture, the feature no spec proposed

Policy OCR shipped 2026-08-01 (5e9cb12) and was documented nowhere. It is
not in INSURANCE_FEATURES_SPEC.md because it did not come from that
meeting — it came out of building the utility statement OCR pipeline in
RECEIPT_CAPTURE_SPEC.md §2 and noticing the same shape fits carrier
policy PDFs. A reader had no way to find that lineage.

New docs/POLICY_OCR.md covers it end to end, with weight on the three
things that are not obvious from the statement side:

- **One PDF = one policy.** Statements arrive bundled one customer per
  page, so there a page is a document. A GMX certificate is one policy
  across two pages, so the pages are concatenated and the parser runs
  once per file — which is why `pageNumber` is a file ordinal and
  `storageKey` is the source PDF, not a page image.
- **The GMX certificate carries no premium at all** — it lives on a
  separate recibo PDF. Hence the null-preserving confirm and the
  double-gated ledger write.
- **OcrModule was extracted out of StatementsModule to make this
  possible**, and that was blocking rather than cosmetic.

Cross-referenced from RECEIPT_CAPTURE_SPEC.md §2 (where it came from),
INSURANCE_FEATURES_SPEC.md (which never proposed it, and whose §4 carrier
API it partly overlaps), PLAN.md step 11, README and RESUME.md.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/RECEIPT_CAPTURE_SPEC.md

@@ -151,6 +151,21 @@ single-movement form.
 > blobs. `GET /statements/status` reports `ocrAvailable` and `storageAvailable`,
 > and the upload card hides itself unless both hold.
 >
+> **This pipeline turned out to generalise, and a second feature came out of
+> it.** Once render → OCR → parse → match → review existed for utility
+> receipts, the same shape obviously fit the *other* stack of paper this
+> office keys in by hand — carrier policy PDFs. That is
+> [`POLICY_OCR.md`](POLICY_OCR.md), built 2026-08-01, and it is **not in any
+> spec**; it was a revelation from doing this one. The `OcrProvider` seam was
+> lifted out of `StatementsModule` into its own `OcrModule` so the policy
+> module could inject it without taking on the statement pipeline —
+> `StatementsModule` imports it now and binds nothing itself. The engine
+> choice stays a one-line change in one file, for both features.
+>
+> One assumption does **not** carry over: statements arrive bundled *one
+> customer per page*, so here a page is a document. A policy PDF is one
+> document across several pages. See that doc's "One PDF = one policy".
+>
 > **Measured, not assumed.** Ten real scans (46 pages of CFE, CESPT and Telnor
 > bills) drove every decision below. Against them the shipped parser identifies
 > the provider on **46/46**, reads an account reference on **43/46**, an amount