feat(shortcuts): regex rewrite rules for host shortcuts

shortcuts.rewrites applies regex replacements after the domain suffix
is stripped, e.g. ^([a-z]+)[0-9]+- -> $1 turns fsn1-bx1.hoster.de into
fsnbx1. The shortcut works for connecting (cached hosts), shell
aliases, and Tab completion, where it is offered when the full name
does not match the typed text. Rules are editable in netssh configure,
and netssh alias --test HOSTNAME shows a name's shortcut and the cached
hosts it matches.

The shortcut lookup only ran when domains or strip_hyphens were set;
it now also runs for rewrite-only configurations.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,8 @@
 - `netssh configure` now covers every setting: after the instances, a menu opens with SSH defaults, SSH options (jump host, host key checking, connection target, address family, extra arguments, `-o` options), SSH rules (add, edit, remove by tag, instance, kind, name pattern), resolver & cache (including the cache file), shortcuts & command alias, and completion (`max_results`). SSH options can also be set per NetBox instance from the instance list.
 - Fix `netssh configure` dropping global SSH options, `ssh.rules`, and `completion.max_results` from the config file when saving.
 - The configurator validates SSH options and rules before writing the config.
+- Add `shortcuts.rewrites`: regex rules that shorten hostnames, e.g. `^([a-z]+)[0-9]+-` → `$1` turns `fsn1-bx1.hoster.de` into `fsnbx1`. Shortcuts work for connecting, shell aliases, and Tab completion (offered when the full name does not match), and can be edited in `netssh configure`.
+- Add `netssh alias --test HOSTNAME` to show the shortcut of a name and the cached hosts it matches.
 
 ## v0.0.22