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-hierarchy/bundle/a/b/doc-b.md

@@ -0,0 +1,6 @@
+---
+type: reference
+title: "Doc B"
+---
+
+Level-2 concept reached depth-first, deepest in the traversal.

examples/nav-golden-hierarchy/bundle/a/b/index.md

@@ -0,0 +1,8 @@
+---
+type: index
+okf_version: 0.1
+title: "Subsection B index"
+---
+
+- [Doc B](doc-b.md)
+- [Back to A](/a/index.md)

examples/nav-golden-hierarchy/bundle/a/doc-a.md

@@ -0,0 +1,6 @@
+---
+type: methodology
+title: "Doc A"
+---
+
+Level-1 concept reached depth-first after Overview.

examples/nav-golden-hierarchy/bundle/a/index.md

@@ -0,0 +1,10 @@
+---
+type: index
+okf_version: 0.1
+title: "Section A index"
+---
+
+- [Doc A](doc-a.md)
+- [Nested verdict](verdict-nested.md)
+- [Subsection B](b/index.md)
+- [Overview again](/overview.md)

examples/nav-golden-hierarchy/bundle/a/verdict-nested.md

@@ -0,0 +1,8 @@
+---
+type: verdict
+title: "Nested verdict — must be excluded"
+decision: approved
+description: "A verdict file at a nested level. A conformant navigator reaches it (dedup marks it seen) but MUST exclude it from the read-context — recursively, not only at the root. This is the leakage surface a graph-based exclusion would miss."
+---
+
+This body MUST NOT appear in the read-context.

examples/nav-golden-hierarchy/bundle/c/orphan.md

@@ -0,0 +1,6 @@
+---
+type: project
+title: "Orphan — unreachable"
+---
+
+Directory `c/` has no `index.md`, and nothing links to this file. A link-following navigator never reaches it; a directory-walking one wrongly would. It MUST be absent from the read-context, and its parent directory's missing `index.md` MUST NOT be an error (that rule binds the bundle root alone).

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

@@ -0,0 +1,10 @@
+---
+type: index
+okf_version: 0.1
+title: "Nav-golden — hierarchical navigation case"
+---
+
+Nav-golden hierarchical case. This bundle exercises depth-first traversal, both link forms (root-relative and relative), recursive verdict exclusion, resolved-path de-duplication, cycle termination, and the root-only binding of the missing-index rule.
+
+- [Overview](overview.md)
+- [Section A](/a/index.md)

examples/nav-golden-hierarchy/bundle/overview.md

@@ -0,0 +1,6 @@
+---
+type: project
+title: "Overview"
+---
+
+Root-level concept reached by a relative link.