fix: move ajv to dependencies and auto-install deps in install scripts

`ajv` is required at runtime by the installer (`scripts/lib/install/config.js`)
but was listed under `devDependencies`. This caused `Error: Cannot find module
'ajv'` when running `./install.sh` from a fresh git clone or via `npx`.

- Move `ajv` from devDependencies to dependencies in package.json
- Add auto `npm install` in install.sh when node_modules is missing
- Add matching auto-install in install.ps1 for Windows parity

install.sh

@@ -14,4 +14,10 @@ while [ -L "$SCRIPT_PATH" ]; do
 done
 SCRIPT_DIR="$(cd "$(dirname "$SCRIPT_PATH")" && pwd)"
 
+# Auto-install Node dependencies when running from a git clone
+if [ ! -d "$SCRIPT_DIR/node_modules" ]; then
+    echo "[ECC] Installing dependencies..."
+    (cd "$SCRIPT_DIR" && npm install --no-audit --no-fund --loglevel=error)
+fi
+
 exec node "$SCRIPT_DIR/scripts/install-apply.js" "$@"