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>

.github/copilot-instructions.md

@@ -0,0 +1,62 @@
+# Gitea Helm Chart — Copilot Instructions
+
+## Project Overview
+
+Kubernetes Helm chart for deploying [Gitea](https://gitea.com). Uses Go/Helm templating (`templates/`), YAML values (`values.yaml`), and includes sub-charts for PostgreSQL, PostgreSQL-HA, Valkey, and Valkey-cluster.
+
+## Build & Test
+
+```bash
+make readme            # Regenerate README.md parameter table + lint
+make unittests-helm    # Run Helm unit tests (helm-unittest plugin required)
+make unittests-bash    # Run bash/bats script tests (requires git submodule init)
+make unittests         # Both of the above
+```
+
+Always run `make readme` after changing `values.yaml` `@param` annotations.
+Always run `make unittests-helm` after changing templates or unit tests.
+
+## Conventions
+
+### values.yaml
+
+- Use `## @param path.to.key Description` annotations for every user-facing value. These drive the auto-generated README parameter table.
+- Property ordering within a resource block: `enabled`, `annotations`, `labels` first, then type-specific fields.
+- Top-level keys are sorted alphabetically within their section group.
+- Use [Helm Values](https://docs.renovatebot.com/modules/manager/helm-values/#additional-information) pattern from renovatebot. Ensure that the attributes `registry`, `repository` and `tag` are available as part of the dict `image`. For example:
+
+```yaml
+image:
+  registry: docker.io
+  repository: library/busybox
+  tag: 0.1.0
+```
+
+### Templates
+
+- Helm templates live in `templates/gitea/`. Helpers live in `templates/_helpers.tpl`.
+- Use camelCase for all files and variables (e.g `httpRoute`, `backendTLSPolicy`, `gatewayAPI`, `statefulSet`).
+- Use `include "gitea.fullname"` for naming resources.
+- Use `fail` for required-value validation with clear error messages referencing the full values path.
+- Ensure, that the attributes `annotations`, `labels`, `name` and `namespace` are alphabetically sorted.
+- Render all attributes, even if they are empty, to prevent drift in Argo CD. For example, `labels` must be rendered, while `annotations` are defined as `yaml:"annotations,omitempty"`.
+- Use plural for `*.tpl` files, because they may contain functions for multiple resources of the same kind (e.g. `_services.tpl` for `httpService.yaml` or `sshService.yaml`, `_backendTLSPolicies.tpl` for `backendTLSPolicy.yaml`).
+
+### Unit Tests
+
+- Helm unit tests live in `unittests/helm/` mirroring the template structure.
+- Test files are YAML using the [helm-unittest](https://github.com/helm-unittest/helm-unittest) format.
+- Each test must set all required values explicitly — do not rely on cross-test state.
+- The `values.yaml` file must pass `yamllint`. The configuration is in `.yamllint`. Use `make yamllint` to run the linter.
+
+### Commits & PRs
+
+- Follow [Conventional Commits](https://www.conventionalcommits.org/en/v1.0.0/) for PR titles and commit messages (e.g. `feat:`, `fix:`, `refactor:`, `docs:`, `style:`).
+- See `CONTRIBUTING.md` for full PR requirements.
+- Explain in detail why a change is needed, not just what the change is. Include links to relevant issues, PRs, or external references.
+- Add co-authors for any contributions that are not your own. Use the `Co-authored-by:` trailer in the commit message.
+
+### Documentation
+
+- `docs/` contains topic-specific guides (e.g. `gateway-api.md`, `ha-setup.md`).
+- `README.md` parameter tables are auto-generated — never edit them manually.