fix(waybar): scope the universal CSS reset to the bar — un-hides tray submenu arrows

BACKLOG #90 root-caused: the arrows were never missing from the icon
theme — Papirus-Dark resolves pan-end-symbolic through its breeze-dark
inheritance (breeze ships inside the nixpkgs papirus output). The real
culprit: Waybar loads its stylesheet screen-wide at application
priority, so the tray menus it hosts for SNI apps (nm-applet & co)
inherit the bar's '* { min-height: 0; }', which out-prioritizes
adw-gtk3's 16px min-height on the menuitem arrow node and collapses
the submenu arrow to zero height. Property bisect confirmed
min-height:0 alone reproduces; the font/border resets don't.

- boreal + executive-slate waybar.css, waybar.nix generatedStyle:
  '*' block scoped to 'window#waybar, window#waybar *'; tooltip rules
  restate the font (tooltips are separate toplevels outside the scope).
- stylix.nix: drop the go-next-symbolic remap — a workaround for the
  misdiagnosis; native pan-end-symbolic resolves fine.
- BACKLOG #90 deleted; JOURNAL entry records the method (live GTK3
  repro + grim screenshots + CSS property bisect, V3 on TuringMachine).

V3 pending: human click on the real nm-applet tray icon post-switch.

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

agent/BACKLOG.md

@@ -28,16 +28,6 @@ in [`docs/ROADMAP.md`](../docs/ROADMAP.md); map in
 
 ## NEXT
 
-### 90. Fix missing submenu arrows in nm-applet `[stuck]`
-**Context:** In Papirus, `pan-end-symbolic` is missing, causing `nm-applet`'s submenu indicator (e.g., "VPN Connections") to be completely invisible.
-**Attempted fixes (2026-07-11):**
-1. Bundled SVG with `-gtk-recolor` (failed due to GTK constraints).
-2. Bundled SVG with static Nix palette colors (failed).
-3. Added `.context-menu` specificity overrides for Waybar SNI tray menus (failed).
-4. Mapped to native `-gtk-icontheme("go-next-symbolic")` instead of bundled SVG (failed).
-**Next steps:** Needs a fresh look. Possibly `dbusmenu-gtk3` drops the arrow entirely or uses a custom widget structure.
-
-
 ### 76. Hibernation default — all agent work shipped `[human]`
 Hibernation + zram on by default (product intent, Bernardo 2026-07-10).
 **All V0/V1/V2 slices done** (2026-07-10); only the V3 check remains.