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

internal/ctr/corebind/registry.go

@@ -0,0 +1,80 @@
+// Package corebind 的契约注册：向开源契约（meshray-contract）注册增强 Bind 工厂与引擎提供方。
+package corebind
+
+import (
+	"sync"
+
+	"git.zkcoi.com/zkcoi/meshray-contract"
+	"git.zkcoi.com/zkcoi/meshray/core/engine"
+	"go.uber.org/zap"
+	"golang.zx2c4.com/wireguard/conn"
+)
+
+// engines 维护 networkID -> Engine 单例映射。
+// EnhancedBind（收发接管）与 engineController（控制面）均通过 networkID 关联同一个 Engine，
+// 使信令下发的候选地址、ICE 配置、层顺序都能落到接管该组网收发的 Engine 上。
+var (
+	enginesMu sync.Mutex
+	engines   = make(map[string]*core.Engine)
+)
+
+// getOrCreateEngine 获取或创建指定组网的 Engine 单例（线程安全）
+func getOrCreateEngine(networkID string, logger *zap.Logger) *core.Engine {
+	enginesMu.Lock()
+	defer enginesMu.Unlock()
+	if e, ok := engines[networkID]; ok {
+		return e
+	}
+	e := core.NewEngine(logger, core.NewMetrics())
+	engines[networkID] = e
+	return e
+}
+
+// engineController 适配 contract.EngineController，以 networkID 关联 Engine 单例，
+// 供管理器在 enhanced 模式调用，无需直接依赖本包具体类型。
+type engineController struct {
+	networkID string
+	engine    *core.Engine
+}
+
+func (c *engineController) Start() error { return c.engine.Start() }
+
+func (c *engineController) Stop() error { return c.engine.Stop() }
+
+// NotifyPeerCandidates 由信令层调用：注入对端候选地址并触发 P2P 建连
+func (c *engineController) NotifyPeerCandidates(peerKey string, candidates []contract.Candidate) error {
+	return c.engine.NotifyPeerInfo(peerKey, toCoreCandidates(candidates))
+}
+
+// SetICEConfig 更新 ICE/STUN/TURN 配置
+func (c *engineController) SetICEConfig(cfg contract.ICEConfig) error {
+	return c.engine.SetICEConfig(toCoreICEConfig(cfg))
+}
+
+// SetLayerOrder 设置传输层优先级顺序（策略核心配置）
+func (c *engineController) SetLayerOrder(order []contract.Layer) error {
+	c.engine.SetLayerOrder(toCoreLayerOrder(order))
+	return nil
+}
+
+// GetStatus 查询引擎状态
+func (c *engineController) GetStatus() (*contract.EngineStatus, error) {
+	st, err := c.engine.GetStatus()
+	if err != nil {
+		return nil, err
+	}
+	return toContractStatus(st), nil
+}
+
+// init 向开源契约注册表注册增强 Bind 工厂与引擎提供方。
+// 由管理器侧 core_enable.go 在 -tags meshray_core 构建下空白导入本包触发，
+// 此时管理器侧 contract.GetBindFactory(true) / NewEngineController 才能取到实现；
+// 默认构建不引入本包，原生直连（默认 Bind）始终可用。
+func init() {
+	contract.RegisterEnhancedBindFactory(func(listenPort int, networkID string, logger *zap.Logger) (conn.Bind, error) {
+		return NewEnhancedBind(listenPort, networkID, logger)
+	})
+	contract.RegisterEngineProvider(func(networkID string, logger *zap.Logger) (contract.EngineController, error) {
+		return &engineController{networkID: networkID, engine: getOrCreateEngine(networkID, logger)}, nil
+	})
+}