feat: Add Infrahub Jinja2 transforms for VLANs, interfaces, and VXLAN (#20) (#24)

## Summary

Closes #20

Adds Infrahub Jinja2 transforms that query device intent from Infrahub via GraphQL and produce structured JSON payloads (YANG-style) suitable for gNMI Set operations on Arista EOS devices.

- **3 GraphQL queries** — `vlan_intent`, `interface_intent`, `vxlan_intent` — each parameterized by `$device_name`
- **3 Jinja2 templates** — `vlan_yang.j2`, `interface_yang.j2`, `vxlan_yang.j2` — producing JSON arrays/objects from the GraphQL response
- **Integration test fixtures** — one directory per transform with `input.json`, `output.json`, and `test.yml`, using leaf1 from the lab topology as sample device
- **`.infrahub.yml` updated** with `queries` and `jinja2_transforms` sections

## Files added

```
transforms/
├── queries/
│   ├── vlan_intent.gql       # VLANs via VTEP mappings + SVI interfaces
│   ├── interface_intent.gql  # All interface types with IPs
│   └── vxlan_intent.gql      # VTEP config + VLAN/VNI/VRF mappings
├── templates/
│   ├── vlan_yang.j2          # JSON array of VLANs (merged, deduplicated, sorted)
│   ├── interface_yang.j2     # JSON array of interfaces with type discriminator
│   └── vxlan_yang.j2         # JSON object: vtep + vlan_vni + vrf_vni mappings
└── tests/
    ├── vlan_yang/{input,output,test}.{json,yml}
    ├── interface_yang/{input,output,test}.{json,yml}
    └── vxlan_yang/{input,output,test}.{json,yml}
```

## Transform usage

```bash
# Render locally
infrahubctl render vlan_yang_transform device_name=leaf1
infrahubctl render interface_yang_transform device_name=leaf1
infrahubctl render vxlan_yang_transform device_name=leaf1

# Via API
GET /api/transform/jinja2/vlan_yang_transform?device_name=leaf1
GET /api/transform/jinja2/interface_yang_transform?device_name=leaf1
GET /api/transform/jinja2/vxlan_yang_transform?device_name=leaf1
```

## Test plan

- [x] Load branch into Infrahub (`infrahubctl schema load` + `infrahubctl object load`)
- [x] Run `infrahubctl render vlan_yang_transform device_name=leaf1` and verify JSON output matches expected VLANs (40, 4090, 4091)
- [x] Run `infrahubctl render interface_yang_transform device_name=leaf1` and verify all interface types are present with correct attributes
- [x] Run `infrahubctl render vxlan_yang_transform device_name=leaf1` and verify VTEP source address, UDP port, and VLAN-VNI mapping for VLAN 40 / VNI 110040
- [x] Run `infrahubctl render vxlan_yang_transform device_name=leaf3` and verify VRF gold / L3VNI 100001 appears in `vrf_vni_mappings`
- ~~[ ] Verify `infrahubctl test` passes for all three test fixtures~~

Reviewed-on: #24

.infrahub.yml

@@ -16,3 +16,25 @@ objects:
   - infrahub/objects/10-bgp-sessions.yml
   - infrahub/objects/11-vrfs.yml
   - infrahub/objects/12-mlag.yml
+
+queries:
+  - name: vlan_intent
+    file_path: infrahub/transforms/queries/vlan_intent.gql
+  - name: interface_intent
+    file_path: infrahub/transforms/queries/interface_intent.gql
+  - name: vxlan_intent
+    file_path: infrahub/transforms/queries/vxlan_intent.gql
+
+jinja2_transforms:
+  - name: vlan_yang_transform
+    description: "Generate VLAN configuration payload from Infrahub intent"
+    query: vlan_intent
+    template_path: infrahub/transforms/templates/vlan_yang.j2
+  - name: interface_yang_transform
+    description: "Generate interface configuration payload from Infrahub intent"
+    query: interface_intent
+    template_path: infrahub/transforms/templates/interface_yang.j2
+  - name: vxlan_yang_transform
+    description: "Generate VXLAN/VTEP configuration payload from Infrahub intent"
+    query: vxlan_intent
+    template_path: infrahub/transforms/templates/vxlan_yang.j2