feat(ecosystem): adopt hub-core dependency and CI pin gate (CORE-WP-0009)

Import slugify_or_default from hub-core, add contract tests, vendor hub-core in
Docker/Forgejo CI, document metadata isolation and pagination deferral, and
align INTENT/SCOPE with three-repo stack.

tests/test_hub_core_imports.py

@@ -0,0 +1,14 @@
+"""Prove hub-core is a pinned, importable consolidation dependency."""
+
+from hub_core.utils.slugs import slugify_or_default
+
+import hub_core
+
+
+def test_hub_core_version_is_pinned() -> None:
+    assert hub_core.__version__ == "0.2.0"
+
+
+def test_slugify_or_default_available_for_api_v2() -> None:
+    assert slugify_or_default("ops-hub") == "ops-hub"
+    assert slugify_or_default("!!!") == "resource"