refactor(build): Replace build tooling with simplified script-based approach

Replace the build toolchain with a cleaner, script-based approach
using just as the task runner:

- hack/build.sh: Unified multi-version build + publish script
- hack/generate-image-manifests.sh: OpenStack Image CRD generator
- hack/generate-resources.sh: ClusterStack + Cluster YAML generator
- hack/show-matrix.sh: Version matrix display tool
- hack/update-addons.sh: Generic addon updater with versions.yaml sync
- hack/docugen.py: Rewritten to accept any stack directory as argument
- justfile: Just task runner (replaces Taskfile.yml)
- Containerfile: Alpine 3.21, pinned tool versions
- flake.nix: Updated dev shell (just instead of task, dropped py3-requests)

Assisted-by: Claude Code
Signed-off-by: Jan Schoone <jan.schoone@uhurutec.com>

Author: jschoone

Containerfile

@@ -0,0 +1,53 @@
+FROM alpine:3.21
+
+LABEL org.opencontainers.image.source="https://github.com/SovereignCloudStack/cluster-stacks"
+LABEL org.opencontainers.image.description="Cluster Stack Build Tools"
+LABEL org.opencontainers.image.licenses="Apache-2.0"
+
+# Install system dependencies
+RUN apk add --no-cache \
+    bash \
+    git \
+    curl \
+    tar \
+    gzip \
+    gawk \
+    python3 \
+    py3-yaml \
+    jq \
+    ca-certificates
+
+# Install helm
+RUN HELM_VERSION=v3.17.3 && \
+    curl -fsSL "https://get.helm.sh/helm-${HELM_VERSION}-linux-amd64.tar.gz" | \
+    tar -xz -C /usr/local/bin --strip-components=1 linux-amd64/helm
+
+# Install yq (mikefarah)
+RUN YQ_VERSION=v4.45.4 && \
+    curl -fsSL "https://github.com/mikefarah/yq/releases/download/${YQ_VERSION}/yq_linux_amd64" \
+    -o /usr/local/bin/yq && chmod +x /usr/local/bin/yq
+
+# Install oras
+RUN ORAS_VERSION=1.2.2 && \
+    curl -fsSL "https://github.com/oras-project/oras/releases/download/v${ORAS_VERSION}/oras_${ORAS_VERSION}_linux_amd64.tar.gz" | \
+    tar -xz -C /usr/local/bin oras
+
+# Install just
+RUN JUST_VERSION=1.40.0 && \
+    curl -fsSL "https://github.com/casey/just/releases/download/${JUST_VERSION}/just-${JUST_VERSION}-x86_64-unknown-linux-musl.tar.gz" | \
+    tar -xz -C /usr/local/bin just
+
+WORKDIR /workspace
+
+# Verify installations
+RUN bash --version | head -1 && \
+    helm version --short && \
+    yq --version && \
+    oras version && \
+    just --version && \
+    git --version
+
+# Allow git operations inside mounted volumes
+RUN git config --global --add safe.directory /workspace
+
+CMD ["/bin/bash"]

flake.lock

@@ -0,0 +1,76 @@
+{
+  description = "Cluster Stacks - Build tools for SCS Kubernetes cluster stacks";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          name = "cluster-stacks-dev";
+
+          buildInputs = with pkgs; [
+            # Core tools
+            bash
+            git
+            curl
+
+            # Container tools
+            docker
+            podman
+
+            # Kubernetes tools
+            kubectl
+            kubernetes-helm
+            kind
+            kustomize
+
+            # Build tools
+            just
+            python3
+            python3Packages.pyyaml
+            jq
+            yq-go
+
+            # OCI/Registry tools
+            oras
+          ];
+
+          shellHook = ''
+            echo "Cluster Stacks development environment"
+            echo ""
+            echo "Available tools:"
+            echo "  just         - Run 'just --list' to see available commands"
+            echo "  helm         - Kubernetes package manager"
+            echo "  kubectl      - Kubernetes CLI"
+            echo "  kind         - Local Kubernetes clusters"
+            echo "  yq           - YAML processor"
+            echo "  oras         - OCI registry client"
+            echo "  python3      - With PyYAML"
+            echo ""
+
+            # Source .env if it exists
+            if [ -f .env ]; then
+              set -a
+              source .env
+              set +a
+              echo "Loaded .env"
+            elif [ -f task.env ]; then
+              set -a
+              source task.env
+              set +a
+              echo "Loaded task.env"
+            else
+              echo "No .env or task.env found. Copy task.env.example to get started."
+            fi
+          '';
+        };
+      }
+    );
+}