desktop: drop the redundant deb depends, correct the pacman docs

Follow-up to 8a8b2b1, driven by what run 2872's new checks actually printed.

The .deb verification did its job on its first run: tauri already infers
exactly libwebkit2gtk-4.1-0 + libgtk-3-0, so declaring the same two in
tauri.conf.json produced a control file listing each of them twice. Removed
the declaration — verify.sh is the real guard, and it fails the build if
inference ever stops covering what the binary links.

The pacman step revealed ci-tauri carries neither zstd nor bsdtar, so packages
currently ship as .pkg.tar.xz with no .MTREE. Both are working outcomes
(pacman reads xz; only `pacman -Qkk` needs .MTREE), but the docs promised
.zst, so the README, the release notes and ci-requirements.md now describe
what the build actually produces.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

desktop/src-tauri/tauri.conf.json

@@ -38,11 +38,6 @@
       "icons/128x128.png",
       "icons/128x128@2x.png",
       "icons/icon.png"
-    ],
-    "linux": {
-      "deb": {
-        "depends": ["libwebkit2gtk-4.1-0", "libgtk-3-0"]
-      }
-    }
+    ]
   }
 }