fix(rofi): drop the go-previous icon from menu Back rows

Every submenu's "↩ Back" row rendered two arrows: the ↩ glyph in the
label plus a themed go-previous icon. back() now emits the plain label
only — identical to what pick-lists already append — so Back shows a
single glyph everywhere. BACK="↩ Back" stays the universal label/match,
so no case-branch comparison changes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -50,12 +50,6 @@ still doesn't open the keybindings cheatsheet. Re-diagnose: confirm the
 Hyprland bind's modmask/keysym against the *actual* layout, whether rofi
 2.0.0 changed anything, and that the cheatsheet path still resolves.
 
-### 34. Menu "Back" shows double arrows `[bug]`
-(Raised by Bernardo, 2026-07-07 — item 4.) The shared `↩ Back` row draws
-a glyph arrow in its label AND an icon arrow — two arrows. Drop one (the
-row icon or the inline glyph) so Back shows a single arrow. One fix in
-the `back`/`row` helper in rofi.nix; applies to every submenu.
-
 ### 40. Display rofi menu "Back" doesn't return `[bug]`
 (Raised by Bernardo, 2026-07-07 — item 10.) In System › Display, the
 Back row fails to return to the previous menu (other submenus' Back work