feat: add APIs to list and download public remote skills (#10448)

Add API to list / download from remote public skills

codex-rs/app-server-protocol/schema/json/v2/SkillsRemoteReadResponse.json

@@ -0,0 +1,37 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "definitions": {
+    "RemoteSkillSummary": {
+      "properties": {
+        "description": {
+          "type": "string"
+        },
+        "id": {
+          "type": "string"
+        },
+        "name": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "description",
+        "id",
+        "name"
+      ],
+      "type": "object"
+    }
+  },
+  "properties": {
+    "data": {
+      "items": {
+        "$ref": "#/definitions/RemoteSkillSummary"
+      },
+      "type": "array"
+    }
+  },
+  "required": [
+    "data"
+  ],
+  "title": "SkillsRemoteReadResponse",
+  "type": "object"
+}