Re-running configure.py keeps every admin host (#891)

[chchatzop]

Fixes #891. Found reviewing #811.

What was wrong

configure.py's services-host question took the first configured ADMIN_HOSTMASKS entry as its default and, on a blank answer, wrote [that one] back. An operator with two hosts (home and phone) who re-ran configure.py and pressed Enter lost the second - silently - and the phone could no longer run admin commands. configure._current()'s own promise is that re-running never does that.

Two smaller faults in the same lines: it indexed the value directly, so a comma-separated string setting (which adminchat accepts) offered its first character as the default; and a wildcard first entry (*!*@*.home.net) was run through the validator as if just typed - Enter printed "That will not do: '*.home.net' has a '*' in it" about a value nobody entered.

What changed

• The hosts are read the way the console itself reads them - adminchat.admin_host_patterns(): either form, deduplicated, host part only - and shown (Configured now: ...), with the prompt saying what blank does.
• A blank answer writes nothing. A host already configured changes nothing. A new host replaces a single configured one, exactly as before; beside several, it is added - one question cannot know which of several a new host replaces - and the operator is told how to remove one.
• INSTALL.md's question list says what a re-run does; both changelogs.

Test

tests/test_a_rerun_of_configure_keeps_every_admin_host.py (8), through collect_answers() with canned input like #811's own tests: two hosts + blank writes nothing (the reported case); one host + blank; typing a host already there (case-insensitively); a new host beside several is added and they are kept; a new host replacing the only one; a wildcard entry is not put through the validator; a comma-separated setting read as hosts; and nothing configured behaving exactly as #811 wrote it. Six fail on the old code; the other two are the cases that deliberately do not change.

Two source guards followed the moved statements: #700's question-order guard anchors on the prompt's new home (a variable, at the same point in the source), and test_a_blank_answer_writes_nothing on the new condition - its property is now also executed by the tests above.

Verified

Full suite on current main: 6429 OK (18 skipped).

🤖 Generated with Claude Code

https://claude.ai/code/session_01AP6LSxkr4n9dMFNSNMogmW

[chchatzop]

Superseded by #909 (merged), which fixed the reported case - Enter no longer collapses the hosts. Two cases this PR covered are still open on main and are filed separately rather than lost: retyping a host that is already configured still replaces all the others, and a comma-separated ADMIN_HOSTMASKS is read as characters. The chain that was stacked on this (#904 -> #905 -> #906) has been rebased onto main.