Prefer default install for shared aliases

[Punisheroot]

Summary

• update_all_shortcuts() now moves the flagged default install to the front before generating global aliases, so shared entrypoints (e.g. pip) resolve to the same runtime as python/pythonw.

Context

BaseCommand.get_installs() keeps precedence order and only sets the default flag for an overridden default (e.g. via PYTHON_MANAGER_DEFAULT). Since create_aliases() is first-match-wins, entrypoint aliases such as pip.exe were claimed by the first install in precedence order, while python/pythonw (yielded only for the default) pointed elsewhere.

Closes #413

Changes

• src/manage/install_command.py: in update_all_shortcuts(), find the default install and move it front (early-break loop, O(1) when already first). Kept local to this function so py list ordering is unchanged, per maintainer direction.
• tests/test_install_command.py: added test_update_all_shortcuts_default_first covering a duplicated alias shared between a first non-default and a second default install.

Validation

• pytest tests/test_install_command.py -q: PASS (25 passed)
• pytest tests/test_install_command.py tests/test_alias.py tests/test_installs.py tests/test_commands.py tests/test_list.py tests/test_uninstall_command.py tests/test_scriptutils.py: PASS (182 passed)
• pytest -q (full suite): PASS (458 passed)
• Repro script for The pip and py/python aliases refer to different installations whenever PYTHON_MANAGER_DEFAULT is anything but the most recent full release available. #413: pre-fix pip from non-default, post-fix pip from default
• New regression test fails without the fix (assert 'new' == 'default') and passes with it
• git diff --check: PASS

Compatibility and risk

• No change to get_installs() ordering, py list, shebang lookup, or python/pythonw handling.
• Only affects the processing order inside update_all_shortcuts(); per-install Start/PEP 514 shortcuts are order-insensitive.

[zooba]

Thanks!