chore: remove DMG guidance from desktop agent instructions

Author: wgqqqqq

src/apps/desktop/AGENTS.md

@@ -89,12 +89,6 @@ The `devtools` Cargo feature exists for debugging UI/UX in the desktop app. When
 
 ## Verification
 
-For DMG background metadata and installer layout, run
-`node --test scripts/desktop-tauri-build.test.mjs` from the repository root.
-Finder interprets the background's physical size: keep the 660×400 PNG at
-72 DPI so it matches the configured window in points. Pixel dimensions alone
-do not guarantee a matching layout.
-
 ```bash
 cargo check -p openbitfun-desktop && cargo test -p openbitfun-desktop
 ```