docs(backlog): scope item 33 (rofi scrollbar) as a ~10-file visual slice

Found every authored .rasi deliberately hides the scrollbar (width:0), so
the overflow hint needs per-theme tuning across ~10 files with a V3-only
payoff — recorded so it is picked up in a themed session, not blind.

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

agent/BACKLOG.md

@@ -248,6 +248,14 @@ onto another page, nothing signals there's more below. Add a scrollbar
 (rofi's `scrollbar` element) or a "more ↓" hint, themed to the palette,
 on the launcher grid and the long text menus. Check rofi 2.0.0's
 scrollbar support/theming.
+_Scoped 2026-07-07:_ rofi only draws the scrollbar when the list actually
+overflows (`lines < rows`), so enabling it self-hides on short menus —
+the right primitive. But it's a **visual, ~10-file slice**: the generated
+palette theme (`rofi.nix`, `scrollbar = false`) **plus every authored
+`.rasi`** (boreal/nord/lumon/kanagawa/retro-82/neon-glass/executive-slate/
+summer-day/summer-night) — all deliberately set `scrollbar { width:0 }`
+today, each needs a per-theme handle width/colour. Payoff is V3-only
+(rendering), so it wants a themed session, not a headless edit.
 
 ### 35. Right-click volume → audio control app
 (Raised by Bernardo, 2026-07-07 — item 5.) Right-click the Waybar