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

Dockerfile

@@ -0,0 +1,23 @@
+FROM golang:1.22-alpine AS builder
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -o proto-gen ./cmd/server
+
+FROM alpine:3.19
+
+RUN apk add --no-cache git ca-certificates
+
+WORKDIR /app
+
+COPY --from=builder /app/proto-gen .
+COPY --from=builder /app/internal/static ./internal/static
+
+EXPOSE 8080
+
+ENTRYPOINT ["./proto-gen"]
+CMD ["--config", "/etc/proto-gen/config.yaml"]