pip install of pyinstaller/pystray/pillow was a separate manual step the
README only mentioned in prose, so the script silently died on missing
packages -- especially bad on Explorer double-click, where the window
closes before any error is visible. Consolidate all dependencies into
requirements.txt (also used by README's plain "pip install -r" flow), have
the script install it itself, wrap the whole build in try/catch with
exit-code checks after every native call, and pause on both success and
failure unless -NoPause is passed.
Also move the build output from %LOCALAPPDATA% into dist/ next to the
script, so it's easy to find and matches the already-gitignored dist/ entry.
