docs: correct two claims the live harness run disproved

The PATH story was wrong in an instructive way. I said a Homebrew Python is on
PATH only because of a shell-profile line; on this host /etc/paths.d/homebrew
puts /opt/homebrew/bin on every login shell's PATH, fresh accounts included.
The stub still wins, because path_helper appends /etc/paths.d/* *after*
/etc/paths and /usr/bin is in the latter. Ordering, not absence, is what makes
bare `python3` the 3.9.6 stub — which is also why the versioned `python3.14`
candidate is the one that matched during the real run, rather than the
/opt/homebrew/bin/python3 fallback I expected.

The harness header also credited install.sh with writing a PATH line into the
login shell. It does not write one. The reset argument is unaffected (such a
line would live in the deleted home either way), but the claim was untrue.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WEfZZhakx13bxTfXcZCoS5

scripts/macos-install-test.sh

@@ -4,8 +4,8 @@
 # Exercises install.sh the way a brand-new user would, inside a throwaway
 # macOS account you create and delete from the CLI. install.sh's entire
 # footprint is user-home-local — the pipx venv under ~/.local (or the pip
-# --user tree under ~/Library/Python), the ~/.bot-bottle config dir, and a
-# PATH line in the login shell. It never installs the backend itself (see
+# --user tree under ~/Library/Python) and the ~/.bot-bottle config dir. It
+# writes no shell-profile PATH line, and never installs the backend (see
 # the header of install.sh), so deleting the user is a complete,
 # deterministic reset of everything the installer touched. The Apple
 # `container` runtime is a HOST prerequisite installed once and kept;