fix(network): 修复长耗时请求被误报「Network disconnected」中断的问题

客户端扩展在慢请求（如提交信息生成）开始约 10 秒后会探测
NetworkService/IsConnected，非 200 应答即判定断网并中止进行中的请求。
此前该探测落入通配路由返回 404，导致模型仍在正常返回时界面先报断连。

- host.go: 注册 IsConnected 精确路由，恒定以 200 + 空 IsConnectedResponse 应答
- client.go: newProtoMessage 补齐 aiserver.v1.IsConnectedResponse 类型，
  避免 mock 编码失败导致探测返回 502
- state_db.go: 新增强开 statsig gate 机制（cursorStateEnabledStatsigGates），
  强制启用 disable_network_change_monitor_local 从源头关闭该探测；
  disableCursorStatsigGates 泛化为 syncCursorStatsigGateOverrides

internal/cursor/state_db.go

@@ -33,6 +33,14 @@ var cursorStateDisabledStatsigGates = []string{
 	"disable_terminal_output_ui_streaming",
 }
 
+// cursorStateEnabledStatsigGates forces gates to true. Disabling the network
+// change monitor stops the always-local extension from probing
+// NetworkService/IsConnected and aborting slow in-flight requests (such as
+// commit message generation) with "Network disconnected".
+var cursorStateEnabledStatsigGates = []string{
+	"disable_network_change_monitor_local",
+}
+
 // InjectCursorUserInfo synchronizes the Cursor user-level auth cache used by the
 // Settings page. It does not modify the installed Cursor app bundle.
 func InjectCursorUserInfo(email, token string) error {
@@ -50,12 +58,13 @@ func InjectCursorUserInfo(email, token string) error {
 	}
 
 	logger.Infof(
-		"injectCursorUserInfo synced path=%s email=%s membership=%s subscription=%s disabled_statsig_gates=%s",
+		"injectCursorUserInfo synced path=%s email=%s membership=%s subscription=%s disabled_statsig_gates=%s enabled_statsig_gates=%s",
 		stateDBPath,
 		values["cursorAuth/cachedEmail"],
 		values["cursorAuth/stripeMembershipType"],
 		values["cursorAuth/stripeSubscriptionStatus"],
 		strings.Join(cursorStateDisabledStatsigGates, ","),
+		strings.Join(cursorStateEnabledStatsigGates, ","),
 	)
 	return nil
 }
@@ -120,7 +129,7 @@ func syncCursorAuthStateDB(path string, values map[string]string) error {
 		}
 	}
 
-	if err := disableCursorStatsigGates(ctx, tx); err != nil {
+	if err := syncCursorStatsigGateOverrides(ctx, tx); err != nil {
 		return err
 	}
 
@@ -131,7 +140,7 @@ func syncCursorAuthStateDB(path string, values map[string]string) error {
 	return nil
 }
 
-func disableCursorStatsigGates(ctx context.Context, tx *sql.Tx) error {
+func syncCursorStatsigGateOverrides(ctx context.Context, tx *sql.Tx) error {
 	var raw []byte
 	err := tx.QueryRowContext(ctx, "SELECT value FROM ItemTable WHERE key = ?", cursorStateStatsigBootstrapKey).Scan(&raw)
 	if err != nil {
@@ -154,9 +163,15 @@ func disableCursorStatsigGates(ctx context.Context, tx *sql.Tx) error {
 
 	hashUsed, _ := payload["hash_used"].(string)
 	for _, gate := range cursorStateDisabledStatsigGates {
-		disableCursorStatsigGate(featureGates, gate)
+		setCursorStatsigGate(featureGates, gate, false, "local_disabled")
 		if strings.EqualFold(hashUsed, "djb2") {
-			disableCursorStatsigGate(featureGates, cursorStateDJB2Hash(gate))
+			setCursorStatsigGate(featureGates, cursorStateDJB2Hash(gate), false, "local_disabled")
+		}
+	}
+	for _, gate := range cursorStateEnabledStatsigGates {
+		setCursorStatsigGate(featureGates, gate, true, "local_enabled")
+		if strings.EqualFold(hashUsed, "djb2") {
+			setCursorStatsigGate(featureGates, cursorStateDJB2Hash(gate), true, "local_enabled")
 		}
 	}
 
@@ -170,21 +185,21 @@ func disableCursorStatsigGates(ctx context.Context, tx *sql.Tx) error {
 	return nil
 }
 
-func disableCursorStatsigGate(featureGates map[string]any, key string) {
+func setCursorStatsigGate(featureGates map[string]any, key string, value bool, rule string) {
 	gate, _ := featureGates[key].(map[string]any)
 	if gate == nil {
 		gate = map[string]any{
 			"name":       key,
-			"rule_id":    "local_disabled",
-			"ruleID":     "local_disabled",
-			"group_name": "local_disabled",
-			"groupName":  "local_disabled",
+			"rule_id":    rule,
+			"ruleID":     rule,
+			"group_name": rule,
+			"groupName":  rule,
 			"id_type":    "userID",
 			"idType":     "userID",
 		}
 		featureGates[key] = gate
 	}
-	gate["value"] = false
+	gate["value"] = value
 }
 
 func cursorStateDJB2Hash(value string) string {