Dock icon: ship the icon as a PNG and refer to it by name (GNOME can't always draw the SVG)

CHANGELOG.md

@@ -10,6 +10,7 @@ one per merged pull request.
 - **feat: GNOME support (the "SteamOS theme for GNOME" option, GDM session switching, the GNOME launcher/notifier/tray behaviour): the Vapor colors, the Steam Deck wallpaper, Ubuntu Dock, Tiling Assistant, Desktop Icons NG, AppIndicator and Steamify's own Vapor shell extension, with Switch to Desktop remembering KDE or GNOME. Prototype work since 2.12.0: `5dfc916`, `fc28ea4`, `ae12c1b`, `2b84e6a`, `c5b59d9`, `62a30e6`, `039f269`, `12eb562`, `c7f5f51`, `7904833`, `ce1aa1b`, `ab3b581`, `eaa3f28`, `4221ae6`, `8432f63`, `09ef0b1`, `68342e7`, `0e0bf57`, `7a84b0d`, `dbaeaa1`**
 - `2ca288d` **fix: the NVIDIA gaming mode setup no longer fails with "the patched gamescope doesn't start" on a gamescope that works: the smoke test judged gamescope's exit status through a pipe into `grep -q` under `pipefail`, so gamescope's crash on the closed pipe (or a hung shutdown) counted as a failed test, intermittently, for the CPU-specific and the generic build alike (seen on an RTX 5080). The test now reads gamescope's output from a file and kills a hung shutdown (`timeout -k`)**
 - `645b331` **feat: the GNOME theme installs GNOME Settings with the "GNOME Desktop" panel (dock, desktop icons, tiling) as a prebuilt package, downloaded from the `settings` release of steamify-gnome-theme (built by GitHub Actions on current Arch, rebuilt weekly) and checked against its `.sha256`; a failure keeps the stock Settings. Turning the theme off puts the stock `gnome-control-center` back. Installs with the GNOME theme on re-apply it (feature version 2.13.0)**
+- **fix: the app's icon shows in GNOME's dock on a fresh install: GNOME couldn't draw the SVG (a blank icon: "Could not load a pixbuf from icon theme"), by path or by name. The app's installer and the launcher put a 256x256 PNG (`assets/steam-gaming-settings.png`, a release file next to the SVG) in the user's icon theme and the launchers refer to it by name; the SVG stays as the fallback for releases without the PNG**
 
 ## 2.12.0 - 2026-10-13