docs(examples): nav-golden fixture class — bundle → read-context goldens

New fixture class for the D4 step-0 split (commons-owned; delivered into
catalog's corpus/runner). A nav-golden case is bundle in / expected-read-
context out — the shape that expresses "two conformant implementations MUST
produce an identical read-context" (method-spec §3 Step 1).

- nav-golden-hierarchy/ (positive): depth-first first-seen order, both link
  forms (/ = bundle root vs relative), one segment per level, resolved-path
  dedup, cycle termination, recursive verdict exclusion, missing-index binds
  root alone, flat render.
- nav-golden-escape/ (negative, gate must go red): .. escapes and a
  /etc/passwd root-relative trap; conformant returns only valid.md.

Both expected-read-context.md verified byte-for-byte against a conformant
navigator implementing §3 Step 1; the negative case verified to diverge
under a naive navigator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VUCuNNvnCkayuUDy2WFgeU

examples/nav-golden-escape/bundle/index.md

@@ -0,0 +1,12 @@
+---
+type: index
+okf_version: 0.1
+title: "Nav-golden — escape / boundary case"
+---
+
+Nav-golden escape case. Every link but the first escapes the bundle or is a root-relative trap; a conformant navigator skips them all, reads none of them, raises nothing, and still returns the one valid sibling.
+
+- [Valid sibling](valid.md)
+- [Parent escape](../SHOULD-NOT-BE-READ.md)
+- [Deep escape](../../../../etc/passwd)
+- [Root-relative trap](/etc/passwd)

examples/nav-golden-escape/bundle/valid.md

@@ -0,0 +1,6 @@
+---
+type: project
+title: "Valid sibling"
+---
+
+The only in-bundle target. A conformant navigator returns exactly this file.