install.sh: stops at an apt prompt, errors on an existing /usr/games, and fails on reinstall #205

install.sh is not safe to run non-interactively or a second time. The following was found by reading the script during the README sweep in #204:

• Line 1: mkdir /usr/games has no -p. On Debian and Ubuntu, /usr/games usually already exists, so this prints File exists. The script has no set -e, so it carries on, but the error looks like a failure.
• Line 4: apt-get install git has no -y. If git isn't installed, this stops at a confirmation prompt. If the prompt is declined, the git clone on line 5 fails and /bin/fishe is still written, pointing at a directory that doesn't exist.
• Line 5: git clone into /usr/games/FishE fails if a previous install is present. The script doesn't point to uninstall.sh or offer a git pull instead.
• There is no shebang, so it depends on being run as sh install.sh / bash install.sh.

Suggested fix: add #!/bin/sh and set -e, use mkdir -p and apt-get install -y git, and skip the clone (or git -C ... pull) when /usr/games/FishE already exists. tests/test_shellEntryPoints.py shows how to assert a script's contract from Python, since the script itself can't be run in CI.

This issue was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

drafted by Claude on behalf of Daniel Stephenson