fix(terminfo): harden systems.configure.terminfo — no silent no-op, sshd validate, required terminfo_hosts

[t0kubetsu]

Summary

Hardens bundles/generic/systems.configure.terminfo (merged via #141), addressing the review feedback that carried over from the superseded #135:

• Drop ignore_errors: true on the terminfo copy — the play now stats /usr/share/terminfo/a/alacritty on the controller first, copies only when present, and emits an explicit skip warning otherwise. Previously a headless controller without Alacritty produced a green run that installed nothing.
• Add validate: '/usr/sbin/sshd -t -f %s' to the sshd_config edit — a config that would not parse is never written, instead of surviving until the next full sshd restart and locking the host out.
• Require terminfo_hosts (drop default('all')) — scenario inventories carry proxmox/proxmox_cli groups, so a caller forgetting the var would rewrite sshd config on the hypervisor and the deployer. Matches the TARGET_GROUP pattern used by the other generic/ bundles. The only existing caller (admin_services_lab stage_01) already passes it explicitly.

README.md and bundle_parameters updated to match (default_where: call-site, no default); JSON regenerated with bundles/_tools/generate-bundle-params.py.

cc @pparage — this picks up your non-blocking findings from #135.

Relates to range42/range42#227.

Not addressed (deliberate)

insertafter: '^AcceptEnv LANG LC_\*' can still fall back to EOF and land inside a trailing Match block on exotic configs. Moving to an /etc/ssh/sshd_config.d/ drop-in would sidestep it, but that changes the bundle's editing strategy — left for a separate change if it bites.

Test plan

• ansible-playbook --syntax-check (ansible-core, -e terminfo_hosts=<group>) — pass
• ansible-lint — the previous ignore-errors violation is gone; the remaining standalone syntax-check[specific] complaint about the undefined hosts var is shared by every templated-hosts bundle in the repo (no lint CI configured)
• Run admin_services_lab stage_01 against the lab; confirm skip warning appears when the controller lacks the terminfo entry, and the copy + sshd reload work when it does