rebuild: split core into separate repo; move wg-go integration to internal/ctr/corebind

- go.mod: require git.zkcoi.com/zkcoi/meshray/core, replace => ../Meshray
- internal/ctr/corebind: EnhancedBind + registry + adapter (wg-go integration isolated)
- cmd/mr-wg migrated from old core/cmd/meshray-core
- core/ removed; CHANGELOG updated; fix checkdb vet warning

cmd/mr-wg/meshray-core.example.json

@@ -0,0 +1,17 @@
+{
+  "network_id": "net1",
+  "listen_port": 51820,
+  "mtu": 1420,
+  "private_key": "",
+  "private_key_file": "key.txt",
+  "interface": "10.0.0.1/24",
+  "mode": "enhanced",
+  "peers": [
+    {
+      "public_key": "<对端机器 -genkey 生成的私钥对应的公钥>",
+      "endpoint": "对端公网IP:51820",
+      "allowed_ips": ["10.0.0.2/32"]
+    }
+  ],
+  "ice": { "stun": [], "turn": [] }
+}