feat(accounting): okf build accounts for every source element

okf build --accounting PATH inventories every source document before
extraction, in the gate's per-format vocabulary, and after the run gives
each element one fate (carried / pointer / coded rejection), written as
JSON and summarised in log.md. "carried" is checked against the written
concept bodies, so a gate that drops a line is found (test). Exit 1 on
anything unaccounted or double-booked. Opt-in: +744 s (+19 %) on the
43-document reference corpus, and that corpus fails the check on 24 real
losses (22 images on text-less PDF pages, 2 docx Title paragraphs).

Changed without the flag:
- okf build exits 1 when it extracted documents and persisted none.
  Door B and corpus.measure are unchanged. One test relied on exit 0.
- An image file carried through a persisted document is its own K1b
  column, no longer also extractor_unknown. The set is what the resolver
  actually carried (ExtractedDocument.files), never a byte match.

tools/okf_accounting_gate.py (checks untouched) is green on all six rows,
R761 110 of 110 under both gates.

Report: docs/2026-09-17-innholdsregnskapet-bygget.md

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

src/llm_ingestion_okf/project.py

@@ -190,10 +190,9 @@ def create(
         bundle_id=identity,
         okf_version=PROJECT_OKF_VERSION,
     )
-    if report.unaccounted or report.merged + report.rejected != report.n:
+    if report.conservation_failed:
         raise IngestError(
-            f"K1b FAILED - merged ({report.merged}) + coded rejections "
-            f"({report.rejected}) != N ({report.n}). Unaccounted: "
+            f"K1b FAILED - {report.identity()}. Unaccounted: "
             f"{', '.join(report.unaccounted) or '(none named)'}",
             code="conservation_failed",
         )