fix: remove helm MCP sidecar and CLI, disable Docker layer cache

- Remove Helm CLI from Dockerfile (OOMKilled sidecar was the only consumer)
- Disable helm MCP sidecar in chart values (uses 194Mi+ idle, OOMKills at 256Mi)
- Remove helm from .mcp.json
- Disable Docker layer cache in build-and-push workflow (cache serves stale
  layers missing tool binaries - DO NOT RE-ENABLE)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -80,12 +80,6 @@ RUN CRUSH_VERSION=$(curl -sL https://api.github.com/repos/charmbracelet/crush/re
     chmod +x /usr/local/bin/crush && \
     rm -rf /tmp/crush*
 
-# Install Helm CLI for Kubernetes chart management
-ARG HELM_VERSION=3.17.1
-RUN curl -fsSL "https://get.helm.sh/helm-v${HELM_VERSION}-linux-amd64.tar.gz" | \
-    tar -xz --strip-components=1 -C /usr/local/bin linux-amd64/helm && \
-    chmod +x /usr/local/bin/helm
-
 # Install GitHub CLI (gh) via official APT repo
 RUN curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg | dd of=/usr/share/keyrings/githubcli-archive-keyring.gpg && \
     chmod go+r /usr/share/keyrings/githubcli-archive-keyring.gpg && \