fix(structure): the index resolves a parent naming a segment of its own document

K3-21 C. `resolve_structure` asks `_segment_lookup` first for a `parent`
edge: `(source_file, segment_id)` -> concept name, keyed off each concept's
own frontmatter (`DocumentStructure.declared`, no file read again), so a
pointer lands only inside the pointing concept's document -- `p1` exists in
every document of a multi-document bundle. A value no segment answers to is a
document number and is looked up exactly as before; a pointer naming nothing
keeps `UNRESOLVED_MARKER`. The rendering rule is untouched: a resolved
relation renders as its subject, so `parent: p1977?` becomes `parent: p1977`.

Moved on purpose, each named: both segmented goldens' index files
(`examples/ingest-golden-segmented{,-okf-v0-2}/expected-bundle/krav/1-{1,2}/
index.md`), whose declared parents s1 and s2 -> s0 rendered `parent: s0?`
while s0 stood in the bundle -- four lines, `?` removed. The four goldens
`test_the_four_existing_goldens_are_untouched` guards are not among them.
`skills/okf-consume/` regenerated, because the golden's index bytes -- and so
its ref -- moved. `test_shell_parent`'s byte test now expects the resolved
facet. README and CLAUDE.md no longer say the index renders it unresolved.

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

skills/okf-consume/references/example-payload.json

@@ -2,7 +2,7 @@
   "contract": "okf-consumption/1",
   "bundle": {
     "bundle_id": "b-golden-segmented-okf-v0-2",
-    "ref": "sha256-tree:f85646c1f77982a69b97afca08209f369b79cd39c217f6f2c074c2dc5bac23fe"
+    "ref": "sha256-tree:cce7a02c769793cdb6e3afda45c955461b57373deab13a986d8bf7843d6e436f"
   },
   "budget": {
     "unit": "utf-8 bytes of emitted JSON",