feat(hyprland): float GTK portal file chooser; close #41

Class xdg-desktop-portal-gtk (+ Nix .…-wrapped) from package desktop/
libexec. Polkit already V3 PASS on Latitude. NEXT only #20 remains.

V0: flake check --no-build green.

agent/BACKLOG.md

@@ -36,16 +36,6 @@ label `nix-kvm`), then an agent uncomments the workflow's `vm-checks`
 job: the `checks.*` VM suite + real toplevel/HM builds on every push
 that later upgrades the bump gate from eval-only to the full suite.
 
-### 41. Floating-window audit — residual GTK portal class `[blocked:hw]`
-(Raised by Bernardo, 2026-07-07 — item 11.) Conservative cut + 2026-07-10
-slice shipped: mixer, blueman, system-config-printer, calendar,
-**hyprpolkitagent** + **pinentry-qt** (classes from package app-id
-strings; softGL capture harness could not materialize dialogs).
-**Still open:** GTK file-chooser portal (`xdg-desktop-portal-gtk`) —
-class not discoverable headlessly. On hardware: open a portal file
-picker, `hyprctl clients`, append float/center rules if needed; confirm
-polkit/pinentry/blueman actually float.
-
 ## LATER
 
 - **Wallpapers artifact split** (ROADMAP § Faster switches — decided,