feat: add scoped assets and storage core

contracts/assets/assets-v1.json

@@ -0,0 +1,28 @@
+{
+  "version": 1,
+  "asset": {
+    "id": "asset-contract-1",
+    "ownerId": "owner-1",
+    "kind": "image",
+    "name": "poster.png",
+    "url": "https://cdn.example.test/uploads/poster.png",
+    "storagePath": "uploads/2026-08-13/poster.png",
+    "source": "upload",
+    "tags": ["upload"],
+    "metadata": { "contentType": "image/png", "size": 4 },
+    "createdAt": "2026-08-13T08:00:00.000Z",
+    "updatedAt": "2026-08-13T08:00:00.000Z"
+  },
+  "defaults": {
+    "platformExternalName": "外部图片",
+    "publicExternalName": "外部素材",
+    "platformExternalTags": ["external"],
+    "publicRequiredTags": ["external", "public-api", "api-client:agent-a"],
+    "platformRegisteredFrom": "api",
+    "publicRegisteredFrom": "public-api"
+  },
+  "publicVisibility": {
+    "jobLookupLimit": 200,
+    "clientTagPrefix": "api-client:"
+  }
+}