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

Makefile

@@ -0,0 +1,19 @@
+BINARY_NAME=proto-gen
+BUILD_DIR=build
+
+.PHONY: all build clean test lint
+
+all: build
+
+build:
+	@mkdir -p $(BUILD_DIR)
+	go build -o $(BUILD_DIR)/$(BINARY_NAME) ./cmd/server
+
+clean:
+	@rm -rf $(BUILD_DIR)
+
+test:
+	go test ./... -v
+
+lint:
+	golangci-lint run ./...