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>

internal/setup/wizard_test.go

@@ -498,3 +498,47 @@ func TestSaveRejectsInvalidSSHOptions(t *testing.T) {
 		t.Fatalf("config file written despite error: %v", err)
 	}
 }
+
+func TestParseRewrites(t *testing.T) {
+	text := `^([a-z]+)[0-9]+- => $1
+
+\.lab$ =>
+`
+	got, err := parseRewrites(text)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []config.ShortcutRewrite{{Pattern: `^([a-z]+)[0-9]+-`, Replace: "$1"}, {Pattern: `\.lab$`, Replace: ""}}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("got %+v", got)
+	}
+	if again, _ := parseRewrites(formatRewrites(got)); !reflect.DeepEqual(again, want) {
+		t.Fatalf("roundtrip: %+v", again)
+	}
+	for _, bad := range []string{"no arrow", "[a- => x", " => x"} {
+		if _, err := parseRewrites(bad); err == nil {
+			t.Errorf("%q accepted", bad)
+		}
+	}
+}
+
+func TestSaveShortcutRewritesRoundtrip(t *testing.T) {
+	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+	t.Setenv("HOME", t.TempDir())
+	rewrites := []config.ShortcutRewrite{{Pattern: `^([a-z]+)[0-9]+-`, Replace: "$1"}, {Pattern: `\.lab\.example\.com$`, Replace: `"q"`}}
+	cfg := config.Config{
+		NetBoxes:  []config.NetBoxConfig{{Name: "prod", URL: "https://prod.example", Token: "t"}},
+		Resolver:  config.ResolverConfig{Strategies: []string{"primary_ip"}},
+		Shortcuts: config.ShortcutsConfig{Rewrites: rewrites},
+	}
+	if err := save(cfg); err != nil {
+		t.Fatal(err)
+	}
+	loaded, err := config.Load()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(loaded.Shortcuts.Rewrites, rewrites) {
+		t.Fatalf("got %+v", loaded.Shortcuts.Rewrites)
+	}
+}