contract(source-project): kind 枚举补 clickable(6c6g 评审待办#1·additive)

clickable = U1 引入的声明式点击基元;原靠 additionalProperties:true 宽松放行(功能可用),此补正把它登记为一等 kind。additionalProperties 维持不变(收紧是独立设计决策,本次只做 additive)。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

contracts/agent-loop/source-project.schema.json

@@ -67,7 +67,7 @@
       "type": "object",
       "required": ["id", "kind"],
       "additionalProperties": true,
-      "properties": { "id": { "type": "string" }, "kind": { "enum": ["render", "collision", "physics", "custom"] } }
+      "properties": { "id": { "type": "string" }, "kind": { "enum": ["render", "collision", "physics", "clickable", "custom"] } }
     },
     "behavior": {
       "type": "object",