feat: add Gateway API support (#1073)

Add full Gateway API support for exposing Gitea via HTTPRoute, TCPRoute, BackendTLSPolicy, and ClientSettingsPolicy resources.

New templates:
- `httpRoute.yaml` — renders an HTTPRoute with configurable
  parentRefs, hostnames, and rules (defaults to PathPrefix `/`)
- `tcpRoute.yaml` — renders a TCPRoute for SSH traffic
- `backendTLSPolicy.yaml` — renders a BackendTLSPolicy for
  encrypted backend connections with required validation config
- `clientSettingsPolicy.yaml` — renders an NGINX Gateway Fabric
  ClientSettingsPolicy to raise the request body size limit

Infrastructure:
- `gatewayAPI.enabled` global toggle gates all resources
- Resources grouped under `gatewayAPI.core.*` and `gatewayAPI.nginx.*`
- Helper templates extracted into dedicated `_*.tpl` files
- Service name helpers (`gitea.service.http.name`, `gitea.service.ssh.name`)
  extracted into `_services.tpl`; service templates renamed to camelCase
- `ROOT_URL`, `DOMAIN`, and `SSH_DOMAIN` auto-resolve from
  `httpRoute.hostnames[0]`; `httpRoute.tls` switches to `https`

Documentation:
- New `docs/gateway-api.md` with topology examples, BackendTLSPolicy
  setup, sectionName guidance, SSH considerations, and NGINX body
  size limit configuration
- `.github/copilot-instructions.md` with project conventions
- README parameter table auto-generated via `make readme`

Tests:
- Helm unit tests for all four new resource templates
- Config tests for hostname/TLS resolution from Gateway API values

Co-authored-by: Todd Marimon <toddmarimon@gmail.com>

unittests/helm/gatewayAPI/clientSettingsPolicy.yaml

@@ -0,0 +1,105 @@
+suite: Test Gateway API clientSettingsPolicy.yaml
+release:
+  name: gitea-unittests
+  namespace: testing
+templates:
+  - templates/gitea/clientSettingsPolicy.yaml
+tests:
+  - it: should not render when gatewayAPI.enabled is false
+    set:
+      gatewayAPI:
+        enabled: false
+        nginx:
+          clientSettingsPolicies:
+            enabled: true
+            body:
+              maxSize: 100m
+    asserts:
+      - hasDocuments:
+          count: 0
+
+  - it: should not render when clientSettingsPolicies.enabled is false
+    set:
+      gatewayAPI:
+        enabled: true
+      gatewayAPI.nginx.clientSettingsPolicies.enabled: false
+    asserts:
+      - hasDocuments:
+          count: 0
+
+  - it: should render a ClientSettingsPolicy targeting the HTTPRoute by default
+    set:
+      gatewayAPI:
+        enabled: true
+        nginx:
+          clientSettingsPolicies:
+            enabled: true
+            body:
+              maxSize: 100m
+    asserts:
+      - hasDocuments:
+          count: 1
+      - isKind:
+          of: ClientSettingsPolicy
+      - equal:
+          path: apiVersion
+          value: gateway.nginx.org/v1alpha1
+      - equal:
+          path: metadata.name
+          value: gitea-unittests
+      - equal:
+          path: spec.targetRef.group
+          value: gateway.networking.k8s.io
+      - equal:
+          path: spec.targetRef.kind
+          value: HTTPRoute
+      - equal:
+          path: spec.targetRef.name
+          value: gitea-unittests
+      - equal:
+          path: spec.body.maxSize
+          value: 100m
+
+  - it: should honor a custom targetRef
+    set:
+      gatewayAPI:
+        enabled: true
+        nginx:
+          clientSettingsPolicies:
+            enabled: true
+            targetRef:
+              group: gateway.networking.k8s.io
+              kind: Gateway
+              name: shared-gateway
+            body:
+              maxSize: 100m
+    asserts:
+      - equal:
+          path: spec.targetRef.kind
+          value: Gateway
+      - equal:
+          path: spec.targetRef.name
+          value: shared-gateway
+
+  - it: should fail when body is missing
+    set:
+      gatewayAPI:
+        enabled: true
+        nginx:
+          clientSettingsPolicies:
+            enabled: true
+    asserts:
+      - failedTemplate:
+          errorMessage: gatewayAPI.nginx.clientSettingsPolicies.body is required
+
+  - it: should fail when body is an empty dict
+    set:
+      gatewayAPI:
+        enabled: true
+        nginx:
+          clientSettingsPolicies:
+            enabled: true
+            body: {}
+    asserts:
+      - failedTemplate:
+          errorMessage: gatewayAPI.nginx.clientSettingsPolicies.body is required