fix(menu): release Left from kb-move-char-back before binding it to Back

rofi hard-fails on a duplicate keybinding and reports it in a GUI error
dialog, not stderr — so 05bab55's Left=Back killed every menu entry
point on a real session while passing all stubbed tests. Rebind
kb-move-char-back to Control+b in both rofi_menu copies (menu + vpn).

V3 on the migrated T14s: error dialog reproduced with old flags, menu
renders with fixed flags. Journal + two PROPOSED pitches (EasyEffects 8
tray icon, parallel fingerprint/password PAM).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/home/rofi.nix

@@ -240,6 +240,10 @@ let
     # the whole menu. Free-text prompts should treat "$BACK" as cancel.
     # Pass --grid as the first arg to skip Left=Back (multi-column theme
     # picker needs Left for column motion).
+    # Left is bound to kb-move-char-back by default and rofi hard-fails
+    # on a duplicate binding (error dialog, no menu) — every binding we
+    # steal must be released from its default first (Ctrl+b remains for
+    # cursor motion in text prompts).
     rofi_menu() {
       local out rc left_back=1
       if [ "''${1:-}" = --grid ]; then
@@ -247,7 +251,8 @@ let
         shift
       fi
       if [ "$left_back" -eq 1 ]; then
-        out=$(command rofi -dmenu -i -kb-custom-1 Left "$@" </dev/stdin)
+        out=$(command rofi -dmenu -i -kb-move-char-back Control+b \
+                           -kb-custom-1 Left "$@" </dev/stdin)
       else
         out=$(command rofi -dmenu -i "$@" </dev/stdin)
       fi
@@ -1207,7 +1212,10 @@ ${themeRows}
     # VPN submenu died with "rofi_menu: command not found").
     rofi_menu() {
       local out rc
-      out=$(command rofi -dmenu -i -kb-custom-1 Left "$@" </dev/stdin)
+      # Release Left from kb-move-char-back first — rofi hard-fails on a
+      # duplicate binding (same fix as the menu's rofi_menu above).
+      out=$(command rofi -dmenu -i -kb-move-char-back Control+b \
+                         -kb-custom-1 Left "$@" </dev/stdin)
       rc=$?
       if [ "$rc" -eq 10 ]; then
         printf '%s\n' "$BACK"