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-fish.fish

@@ -69,6 +69,10 @@ function pipx
     wrapSafeChainCommand "pipx" $argv
 end
 
+function pdm
+    wrapSafeChainCommand "pdm" $argv
+end
+
 function printSafeChainWarning
     set original_cmd $argv[1]