refactor(ingest): adopt shared llm-ingestion-okf v0.3.1 behind a thin adapter

Door A (manifest -> connector -> deterministic materialization -> index) is no
longer implemented here. src/portfolio_optimiser/ingest.py becomes a thin
consumer seam over the shared library, git-pinned to v0.3.1 on the same Forgejo
channel portfolio-optimiser-claude uses. Net -626/+385; ingest.py 599 -> 145 lines.

shared/ingest-spec.md remains the normative spec: the library implements it, it
does not replace it. Spec changes continue to go via commons.

Acceptance criterion met and proven: all three golden bundles (file/sql/http)
are byte-exact before and after, including the idempotence re-run. examples/ and
shared/ carry ZERO modifications -- the fasit was not adjusted to fit.

The rejection set was verified equivalent, not assumed: all 22 malformations the
repo's pydantic models refused are refused by the library, with typed codes
(okf_type_reserved, credential_embedded, extraction_id_duplicate, ...).

Test rebinding (invariants preserved, vehicle changed): the library has zero
runtime dependencies by design, so pydantic is unavailable to it.
ManifestV1.model_validate(dict) -> load_manifest_bytes(bytes); ValidationError ->
ManifestError; model_fields -> dataclasses.fields; PathSecurityError ->
SourceError(path_escape); ValueError -> MaterializationError(ingested_at_invalid).
Tests now also pin the refusal `code`, the library's documented stability
contract -- a sharper assertion than "some validation error was raised".

Two accepted behavioural deltas, recorded rather than silently dropped:
- Title whitespace is stored verbatim instead of collapsed at validation, so the
  frontmatter title and the index label are no longer guaranteed identical for
  irregular whitespace. Both behaviours are spec-conformant (the spec is SILENT;
  the old one was a repo-local pinned decision). Queued as a commons-amendment
  candidate so both stacks pin the same answer. Goldens unaffected.
- The section 8 audit log moves to logger llm_ingestion_okf.materialize. Nothing
  in the repo consumed the old channel.
Also: the `type` discriminator is no longer a dataclass field, so the spec
cross-check asserts it explicitly -- without that line the swap would have
silently narrowed the test.

New tests/test_ingest_library_seam.py pins the seam itself: the restated section 5
stamp formula against the stamp the library actually writes (the one place the
adapter does not purely delegate, since v0.3.1 exposes no stamp helper), the
local-only allow_network default, the list[Path] unwrapping, and a guard that the
adapter never regrows local Door A machinery. All four verified RED when detached,
as were both golden regressions under a byte-level render mutation.

Door A is UNGATED: it calls no guard before writing to disk. Gating untrusted
content remains the caller's responsibility (guard wiring still planned).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B4jNN186eVqfe1x5DnTU6r

tests/test_method_spec_loadbearing.py

@@ -12,6 +12,7 @@ drifts away from what the spec documents.
 
 from __future__ import annotations
 
+import dataclasses
 import json
 import re
 from pathlib import Path
@@ -187,7 +188,7 @@ def test_ingest_spec_documents_every_contract_field() -> None:
     def documented(field: str, source: str) -> None:
         assert f"`{field}`" in text, f"ingest spec does not document {source} field `{field}`"
 
-    for field in ManifestV1.model_fields:
+    for field in (f.name for f in dataclasses.fields(ManifestV1)):
         documented(field, "manifest top-level")
     for model, source in (
         (FileSource, "file source"),
@@ -195,8 +196,13 @@ def test_ingest_spec_documents_every_contract_field() -> None:
         (HttpSource, "http source"),
         (Extraction, "extraction"),
     ):
-        for field in model.model_fields:
+        for field in (f.name for f in dataclasses.fields(model)):
             documented(field, source)
+    # The library's source models consume the `type` discriminator during validation dispatch
+    # instead of storing it as a field, so it is no longer reachable by introspection. It is a
+    # REAL §4 contract field, so it is asserted explicitly — without this line the swap from
+    # `model_fields` to `dataclasses.fields` would silently drop it from the cross-check.
+    documented("type", "source discriminator")
 
     # The §5/§7 provenance layer — exactly the keys the materializer stamps.
     for key in (