fix: don't rely on file sort for fallback deps

production dependencies are injected as fallback into the environment
but can be overridden by a simple pip install

this fix is designed to ensure that the last position in sys.path
does not depend on the file system ordering of any particular
implementation but instead injects itself last explicitly, cause
evaluation of python code inside .pth files happens lazily

src/shell.nix

@@ -196,7 +196,7 @@ in {
                      ${lib.getExe python} -m venv "$PRJ_DATA_HOME/pyenv";
                     "$PRJ_DATA_HOME/pyenv/bin/python" -m pip install --quiet --upgrade pip
                   }
-                  echo "${penv}/${sitePackagesPath}" > "$PRJ_DATA_HOME/pyenv/${sitePackagesPath}/zzz-shell-python-env.pth"
+                  echo 'import sys; sys.path.append("${penv}/${sitePackagesPath}")' > "$PRJ_DATA_HOME/pyenv/${sitePackagesPath}/frappix-prod-deps-fallback.pth"
                 '';
               deps = ["emplace-folders" "ensure-env-vars"];
             };