Add pdm package manager support

PDM is a modern Python package manager using pyproject.toml (PEP 621).
Uses the same MITM-only proxy approach as poetry/uv/pipx — all malware
detection and minimum package age enforcement happens at the proxy layer
by intercepting PyPI requests.

packages/safe-chain/src/shell-integration/startup-scripts/init-posix.sh

@@ -65,6 +65,10 @@ function pipx() {
   wrapSafeChainCommand "pipx" "$@"
 }
 
+function pdm() {
+  wrapSafeChainCommand "pdm" "$@"
+}
+
 function printSafeChainWarning() {
   # \033[43;30m is used to set the background color to yellow and text color to black
   # \033[0m is used to reset the text formatting