node/: install Node.js for npx

The MCP servers in mcp-config/ are npm packages that opencode spawns as
`npx -y <pkg>`. Without npx on PATH they all fail to start, and opencode
reports that only as a dead server -- easy to misread as a broken config.

Node is a tree, not a single binary, so it follows the ansible module:
unpack under ~/.local/opt and symlink the CLIs into ~/.local/bin.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

node/install.sh

@@ -0,0 +1,62 @@
+#!/usr/bin/env sh
+# node/install.sh — install Node.js (and with it npx) into userland.
+#
+# WHY: the MCP servers in mcp-config/opencode.gateway.json are npm packages and
+# opencode spawns them as `npx -y <pkg>@<version>`. Without npx on PATH every
+# MCP server fails to start with "command not found" — and opencode reports that
+# only as a dead server, so it is easy to misread as a broken config. The MCP
+# ecosystem is overwhelmingly npx-based, so this also unblocks future servers.
+#
+# Node is a tree (bin/node + lib/node_modules/npm), not a single binary, so it
+# cannot use bin/install.sh's install_tarball_bin. It follows the ansible module
+# instead: unpack under ~/.local/opt and symlink the CLIs into ~/.local/bin.
+# Everything is under $HOME — no sudo, and it survives a Kasm redeploy.
+set -eu
+
+SCRIPT_DIR="$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)"
+REPO_ROOT="$(dirname -- "$SCRIPT_DIR")"
+
+# shellcheck source=../lib/fetch.sh
+. "$REPO_ROOT/lib/fetch.sh"
+
+say() { printf '%s\n' "$*" >&2; }
+
+# Pinned LTS. Bump deliberately: npx executes whatever the registry serves, so
+# the runtime is part of the supply chain that sees your Gitea/Proxmox tokens.
+NODE_VERSION="v24.18.0"
+
+PREFIX="$HOME/.local/opt/node"
+BIN_DIR="$HOME/.local/bin"
+NODE_CLIS="node npm npx"
+
+case "$(fetch_arch)" in
+  x86_64)  NODE_ARCH=x64 ;;
+  aarch64) NODE_ARCH=arm64 ;;
+  *)       say "node: unsupported arch $(fetch_arch)"; exit 1 ;;
+esac
+
+# Verify it RUNS, not just that the file exists: a Kasm redeploy can leave a
+# present-but-broken tree behind (same failure the ansible venv guards against).
+if [ "$("$PREFIX/bin/node" --version 2>/dev/null || true)" = "$NODE_VERSION" ]; then
+  say "node $NODE_VERSION already present at $PREFIX."
+else
+  TARBALL="node-$NODE_VERSION-linux-$NODE_ARCH.tar.gz"
+  URL="https://nodejs.org/dist/$NODE_VERSION/$TARBALL"
+  TMP="$(mktemp -d)"
+  say "Installing node $NODE_VERSION ($NODE_ARCH) into $PREFIX..."
+  _fetch_dl "$URL" "$TMP/node.tar.gz"
+  rm -rf "$PREFIX"
+  mkdir -p "$PREFIX"
+  # The archive has a single top-level dir; strip it so bin/ lands at $PREFIX/bin.
+  tar -xzf "$TMP/node.tar.gz" -C "$PREFIX" --strip-components=1
+  rm -rf "$TMP"
+  say "Installed node $NODE_VERSION."
+fi
+
+# Symlink the CLIs into ~/.local/bin (on PATH via zsh/zshrc). npx must be here:
+# opencode spawns MCP servers with a bare `npx`, resolved from PATH.
+mkdir -p "$BIN_DIR"
+for cli in $NODE_CLIS; do
+  [ -x "$PREFIX/bin/$cli" ] && ln -sf "$PREFIX/bin/$cli" "$BIN_DIR/$cli"
+done
+say "Linked node CLIs ($NODE_CLIS) into $BIN_DIR."