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

tools/chemenu/tests/test_index_build.py

@@ -6,6 +6,7 @@ from chemenu.commands.index_build import (
     SHARD_THRESHOLD,
     _anchor,
     build_index,
+    index_rebuild,
     plan_index,
     stale_shards,
 )
@@ -202,3 +203,25 @@ def test_scanner_ignores_generated_shards_at_any_depth(kb_dir, plan):
 
 def test_rebuild_is_idempotent(kb_dir):
     assert plan_index(kb_dir) == plan_index(kb_dir)
+
+
+def test_rebuild_warns_about_a_nested_page_without_failing(kb_dir, capsys):
+    """#57: `group_pages` still folds a nested page into its area silently -
+    that part is unchanged, reporting is the fix - so `index rebuild` warns
+    rather than refusing, and must not raise."""
+    write_page(
+        kb_dir / "entities/projects/someowner/nested-tool.md",
+        {"type": "types/entity.md", "entity_type": "project", "tags": [],
+         "created": "2026-07-25", "modified": "2026-07-25",
+         "related": [], "sources": [], "confidence": 0.8},
+        "\n# nested-tool\n",
+    )
+    index_rebuild(dry_run=False)
+    out = capsys.readouterr().out
+    assert "WARNING" in out
+    assert "nested-tool" in out
+
+
+def test_rebuild_is_silent_about_a_healthy_tree(kb_dir, capsys):
+    index_rebuild(dry_run=False)
+    assert "WARNING" not in capsys.readouterr().out