nested_pages: Katalogtiefe 1 durchgesetzt, layout:-dir validiert, move raeumt geleerte Verzeichnisse - die drei #57-Seiten hochgezogen (schliesst #57)

Files changed:
- CHANGES.md
- VERSION
- kb/CONTRACT.md
- kb/entities/projects/kfchou/wiki-skills.md
- kb/entities/projects/llm-wiki-skills.md
- kb/entities/projects/vanillaflava/wiki-skills-vanillaflava.md
- kb/entities/projects/wiki-skills-vanillaflava.md
- kb/entities/projects/wiki-skills.md
- kb/entities/projects/yugasun/llm-wiki-skills.md
- kb/log.md
- tools/CONTRACT.md
- tools/chemenu/commands/index_build.py
- tools/chemenu/commands/page_ops.py
- tools/chemenu/kb_scan.py
- tools/chemenu/lint_core.py
- tools/chemenu/tests/test_index_build.py
- tools/chemenu/tests/test_kb_scan.py
- tools/chemenu/tests/test_lint.py
- tools/chemenu/tests/test_page_ops.py
- tools/chemenu/tests/test_type_resolver.py
- tools/chemenu/type_resolver.py

kb/CONTRACT.md

@@ -46,6 +46,16 @@ resolves against it by name.
 - A subdirectory *inside* a collection is an **area**. It inherits the enclosing contract and
   must not carry a `COLLECTION.md` of its own - `kb/entities/systems/` is an area of
   `kb/entities/`.
+- **An area is as deep as a page goes.** `kb/<collection>/<page>.md` and
+  `kb/<collection>/<area>/<page>.md` are the two depths a page may sit at; nothing goes a level
+  deeper. A further subdirectory is not a second-level area - it is invisible to the generated
+  catalog, which reads exactly two path segments below `kb/` and folds anything past them into
+  the area's own table silently, with no location of its own (Gitea #57). That is why
+  `wikitool lint`'s `nested_pages` finding is a hard error rather than an advisory one like
+  `misplaced_pages`: a misplaced page still catalogs correctly from the wrong place, a nested
+  one makes the catalog itself wrong. A grouping axis that does not come from a type-spec's
+  `layout:` - project owner was the case that surfaced this - does not earn a second directory
+  level; it goes into frontmatter instead.
 - A `COLLECTION.md` nested inside another collection is invalid.
 - `COLLECTION.md` appears **nowhere outside `kb/`**. `raw/`, `types/`, `tools/`, `reports/`
   and `instructions/` are not collections and carry a `CONTRACT.md` or a root type-spec