feat: implement proto-gen platform

- Config loader with env var expansion and validation
- SQLite database with tasks and toolchain_versions tables
- Gitea REST API client for repository and branch operations
- K8s client for Job lifecycle management (with noop fallback for local dev)
- REST API: tasks CRUD, retry, plugins, version management
- Worker/scheduler with polling, concurrency control, and job tracking
- Static frontend: generate, tasks, settings pages
- Toolchain images: Go and Node.js Dockerfiles with entrypoint scripts
- Helm chart with deployment, service, configmap, ingress, PVC
- Multi-stage Dockerfile for service
- Unit tests for config, database, gitclient, k8s, api, worker
- E2E tests for idempotency, version switch, failure recovery

internal/gitclient/interface.go

@@ -0,0 +1,21 @@
+package gitclient
+
+type Repository struct {
+	Name     string `json:"name"`
+	FullName string `json:"full_name"`
+	Private  bool   `json:"private"`
+	Empty    bool   `json:"empty"`
+}
+
+type Branch struct {
+	Name   string `json:"name"`
+	Commit string `json:"commit"`
+}
+
+type GitClient interface {
+	ListRepositories(owner string) ([]Repository, error)
+	CreateRepository(owner, name, description string, private bool) (*Repository, error)
+	GetRepository(owner, name string) (*Repository, error)
+	ListBranches(owner, repo string) ([]Branch, error)
+	GetBranch(owner, repo, branch string) (*Branch, error)
+}