pip_user_install: add --break-system-packages on Ubuntu 24.04+

pip3 install --user alone does not reliably bypass PEP 668 in all 24.04
environments. --break-system-packages (pip 22.3+) is the correct override.
Flag is only added when ubuntu_version_ge "24.04" so it does not run on
Ubuntu 22.04 where pip 22.0 ships and the flag is not yet supported.

https://claude.ai/code/session_01Y4dMKtkqkpvmgDKoRdzhTG

lib/common.sh

@@ -124,9 +124,12 @@ ubuntu_version_ge() {
 }
 
 # pip install --user as actual user.
-# Centralised so any future version-specific pip flags land in one place.
+# --break-system-packages (pip 22.3+) is required on Ubuntu 24.04+ where PEP 668
+# marks the system Python as externally managed; --user alone is not always enough.
 pip_user_install() {
-    sudo -u "$ACTUAL_USER" pip3 install --user --quiet "$@"
+    local flags="--user --quiet"
+    ubuntu_version_ge "24.04" && flags="$flags --break-system-packages"
+    sudo -u "$ACTUAL_USER" pip3 install $flags "$@"
 }
 
 detect_os