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/models.py

@@ -0,0 +1,10 @@
+from dataclasses import dataclass
+from typing import Any
+
+
+@dataclass
+class EntitlementResult:
+    allow: bool
+    reason: str = ""
+    expire_at: str = ""
+    raw: dict[str, Any] | None = None