feat(config-settings): shared four-page tab header helper

functions/__config_settings_pagetab.fish

@@ -0,0 +1,43 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# SYNOPSIS
+#   __config_settings_pagetab <active_idx> <iw>
+#
+# DESCRIPTION
+#   Renders the four-page tab strip used as the header line of every
+#   config-settings page. Pages: 0 Universal, 1 Session, 2 Sponge, 3 Paths.
+#   The active page is marked with a filled bullet and bold text; the others
+#   with a hollow bullet. The returned string is padded to exactly <iw>
+#   printable columns (the caller adds the │ │ border and center offset).
+#
+# ARGUMENTS
+#   active_idx  0–3, the active page index
+#   iw          inner width in columns to pad the strip to
+#
+# RETURNS
+#   0  Always; prints the tab strip (no trailing newline beyond printf's)
+#
+# EXAMPLE
+#   set strip (__config_settings_pagetab 2 76)
+function __config_settings_pagetab
+    set -l active $argv[1]
+    set -l iw     $argv[2]
+
+    set -l c_hi    (set_color --bold white)
+    set -l c_reset (set_color normal)
+    set -l names Universal Session Sponge Paths
+
+    set -l strip ' '
+    for i in (seq 0 3)
+        set -l idx (math $i + 1)
+        if test $i -eq $active
+            set strip "$strip$c_hi●$names[$idx]$c_reset  "
+        else
+            set strip "$strip○$names[$idx]  "
+        end
+    end
+    # string pad is width-aware: color escapes count as 0 columns, the bullets
+    # and letters as their printable width.
+    string pad -r -w $iw -- $strip
+end