Align the Comment Copies the Sentence Sweep Split Two Ways, and Fix Three Stale Counts #3622

Follow-ups left by the #3531 sentence-length comment sweep (round 5 of #3575). Each is small, and none fails a gate today.

1. Align comment copies that two slices split differently

Slice F1 (#3612) and slice F2 (#3613) ran in parallel. Each split its own copy of a shared comment, so the copies now read differently, though both pass sentence-length. Find the original in develop before #3612 and #3613, and give every copy one wording:

• "Every probe refuses to write a host key" and "A native command writes to this function": split in host-setup/bootstrap.ps1. Copies are in host-setup/windows/install-agents.ps1, install-tools.ps1, and setup-wsl.ps1.
• The WSL_UTF8 comment: split in host-setup/windows/upgrade-host.ps1, with a copy near host-setup/windows/setup-wsl.ps1:121.
• "A script parameter reached only from a nested scope" and "Under pipefail": F2 reported copies outside its slice without locating them. Grep for them.

2. Comment counts that were already wrong

Each of these comments states a count that does not match what follows it. Each predates the sweep, which left it unchanged:

• "the four functions below" in host-setup/bootstrap.ps1 and host-setup/menu.ps1
• "the four scripts" in tests/test_bootstrap.py

Fix each count against the code, or drop it, since a stated count goes stale.

3. Rollout-history wording in scripts/README.md

#3621 removed one past-tense sentence about sentence-length shipping opt-in. The review pass noted similar rollout wording near lines 62 and 66. Rewrite it in the present tense if it describes history rather than the current mechanism. docs/fleet-map.md's dated decision record is deliberately historical, so leave it.