feat(core): implement namespace support and routing bindings

Introduce namespace-aware routing capabilities through a new Binding
model and updates to Master/Key entities.

- Add Binding model for configuring model routes per namespace
- Add DefaultNamespace and Namespaces fields to Master and Key models
- Update auto-migration to include Binding table
- Implement Redis synchronization for binding configurations
- Propagate namespace settings during master creation and key issuance

internal/service/master.go

@@ -46,6 +46,8 @@ func (s *MasterService) CreateMaster(name, group string, maxChildKeys, globalQPS
 		MasterKey:       string(hashedMasterKey),
 		MasterKeyDigest: masterKeyDigest,
 		Group:           group,
+		DefaultNamespace: "default",
+		Namespaces:       "default",
 		MaxChildKeys:    maxChildKeys,
 		GlobalQPS:       globalQPS,
 		Status:          "active",
@@ -150,10 +152,18 @@ func (s *MasterService) issueChildKey(masterID uint, group string, scopes string
 		TokenHash:     tokenHash,
 		Group:         group,
 		Scopes:        scopes,
+		DefaultNamespace: strings.TrimSpace(master.DefaultNamespace),
+		Namespaces:       strings.TrimSpace(master.Namespaces),
 		IssuedAtEpoch: master.Epoch,
 		Status:        "active",
 		IssuedBy:      strings.TrimSpace(issuedBy),
 	}
+	if strings.TrimSpace(key.DefaultNamespace) == "" {
+		key.DefaultNamespace = "default"
+	}
+	if strings.TrimSpace(key.Namespaces) == "" {
+		key.Namespaces = key.DefaultNamespace
+	}
 	if key.IssuedBy == "" {
 		key.IssuedBy = "master"
 	}