feat: add jiangchang platform kit skeleton

Add a shared SDK scaffold for entitlement checks and a reusable Gitea release workflow template to standardize skill packaging and publishing across projects.

sdk/jiangchang_skill_core/guard.py

@@ -0,0 +1,22 @@
+from .client import EntitlementClient
+from .errors import EntitlementDeniedError
+from .models import EntitlementResult
+
+
+def enforce_entitlement(
+    user_id: str,
+    skill_slug: str,
+    trace_id: str = "",
+    context: dict | None = None,
+    client: EntitlementClient | None = None,
+) -> EntitlementResult:
+    c = client or EntitlementClient()
+    result = c.check_entitlement(
+        user_id=user_id,
+        skill_slug=skill_slug,
+        trace_id=trace_id,
+        context=context or {},
+    )
+    if not result.allow:
+        raise EntitlementDeniedError(result.reason or "skill not purchased or expired")
+    return result