feat(schema): add VRF schema

Add models for VRF, Route Target, and VRF-Device assignments.
Supports L3VNI association for symmetric IRB routing.

Ref: #41

schemas/vrf.yml

@@ -0,0 +1,109 @@
+# VRF Schema for EVPN-VXLAN Fabric
+# Defines VRF and Route Target configuration for L3 VPN
+---
+version: "1.0"
+nodes:
+  # =============================================================================
+  # VRF (Virtual Routing and Forwarding)
+  # =============================================================================
+  - name: VRF
+    namespace: Infra
+    description: Virtual Routing and Forwarding instance
+    label: VRF
+    icon: mdi--router
+    default_filter: name__value
+    order_by:
+      - name__value
+    display_labels:
+      - name__value
+    attributes:
+      - name: name
+        kind: Text
+        description: VRF name
+      - name: description
+        kind: Text
+        optional: true
+      - name: rd
+        kind: Text
+        optional: true
+        description: "Route Distinguisher (format: ASN:NN or IP:NN)"
+      - name: vrf_id
+        kind: Number
+        optional: true
+        description: VRF table ID
+    relationships:
+      - name: l3vni
+        peer: InfraVNI
+        cardinality: one
+        optional: true
+        description: L3 VNI for symmetric IRB
+      - name: import_targets
+        peer: InfraRouteTarget
+        cardinality: many
+        optional: true
+      - name: export_targets
+        peer: InfraRouteTarget
+        cardinality: many
+        optional: true
+      - name: interfaces
+        peer: InfraInterface
+        cardinality: many
+        optional: true
+        description: Interfaces assigned to this VRF
+
+  # =============================================================================
+  # Route Target
+  # =============================================================================
+  - name: RouteTarget
+    namespace: Infra
+    description: BGP Route Target for VPN import/export
+    label: Route Target
+    icon: mdi--target
+    default_filter: target__value
+    order_by:
+      - target__value
+    display_labels:
+      - target__value
+    attributes:
+      - name: target
+        kind: Text
+        unique: true
+        description: "Route Target value (format: ASN:NN or IP:NN)"
+      - name: description
+        kind: Text
+        optional: true
+
+  # =============================================================================
+  # VRF Device Assignment
+  # =============================================================================
+  - name: VRFDeviceAssignment
+    namespace: Infra
+    description: VRF assignment to a specific device
+    label: VRF Assignment
+    icon: mdi--router-network
+    display_labels:
+      - vrf__name__value
+      - device__name__value
+    attributes:
+      - name: rd
+        kind: Text
+        optional: true
+        description: "Device-specific RD (overrides VRF default)"
+    relationships:
+      - name: vrf
+        peer: InfraVRF
+        cardinality: one
+      - name: device
+        peer: InfraDevice
+        cardinality: one
+        kind: Parent
+      - name: import_targets
+        peer: InfraRouteTarget
+        cardinality: many
+        optional: true
+        description: Device-specific import RTs
+      - name: export_targets
+        peer: InfraRouteTarget
+        cardinality: many
+        optional: true
+        description: Device-specific export RTs