fix(desktop): improve Linux desktop icon integration (#334)

Refs #330

## Summary
- add standard Linux hicolor icon sizes to the Tauri package outputs
- enable the GTK app id on Linux and ship a matching reverse-DNS desktop
entry alias for shell association
- mark the alias desktop entry `NoDisplay=true` so it does not surface
as a duplicate launcher in desktop menus
- include the same alias desktop entry for AppImage so the fix is not
limited to deb/rpm packages

## Validation
- confirmed in the Linux VM that the desktop-integrated launch no longer
shows the generic taskbar icon
- verified the alias desktop entry is now hidden from app menus via
`NoDisplay=true`
- attempted a fresh `tauri build --bundles deb`; the build still hits
the known optional `@tauri-apps/cli` native-binding issue in this
workspace after prebuild, not a code/config error from this PR

packages/tauri-app/src-tauri/icons/linux/ai.neuralnomads.codenomad.client.desktop

@@ -0,0 +1,9 @@
+[Desktop Entry]
+Categories=
+Exec=codenomad-tauri
+StartupWMClass=codenomad-tauri
+Icon=codenomad-tauri
+Name=CodeNomad
+NoDisplay=true
+Terminal=false
+Type=Application

packages/tauri-app/src-tauri/tauri.conf.json

@@ -9,6 +9,7 @@
     "frontendDist": "resources/ui-loading"
   },
   "app": {
+    "enableGTKAppId": true,
     "withGlobalTauri": true,
     "windows": [
       {
@@ -41,6 +42,35 @@
   },
   "bundle": {
     "active": true,
+    "linux": {
+      "appimage": {
+        "files": {
+          "/usr/share/applications/ai.neuralnomads.codenomad.client.desktop": "icons/linux/ai.neuralnomads.codenomad.client.desktop"
+        }
+      },
+      "deb": {
+        "files": {
+          "/usr/share/applications/ai.neuralnomads.codenomad.client.desktop": "icons/linux/ai.neuralnomads.codenomad.client.desktop",
+          "/usr/share/icons/hicolor/32x32/apps/codenomad-tauri.png": "icons/linux/32x32.png",
+          "/usr/share/icons/hicolor/48x48/apps/codenomad-tauri.png": "icons/linux/48x48.png",
+          "/usr/share/icons/hicolor/64x64/apps/codenomad-tauri.png": "icons/linux/64x64.png",
+          "/usr/share/icons/hicolor/128x128/apps/codenomad-tauri.png": "icons/linux/128x128.png",
+          "/usr/share/icons/hicolor/256x256/apps/codenomad-tauri.png": "icons/linux/256x256.png",
+          "/usr/share/icons/hicolor/512x512/apps/codenomad-tauri.png": "icons/linux/512x512.png"
+        }
+      },
+      "rpm": {
+        "files": {
+          "/usr/share/applications/ai.neuralnomads.codenomad.client.desktop": "icons/linux/ai.neuralnomads.codenomad.client.desktop",
+          "/usr/share/icons/hicolor/32x32/apps/codenomad-tauri.png": "icons/linux/32x32.png",
+          "/usr/share/icons/hicolor/48x48/apps/codenomad-tauri.png": "icons/linux/48x48.png",
+          "/usr/share/icons/hicolor/64x64/apps/codenomad-tauri.png": "icons/linux/64x64.png",
+          "/usr/share/icons/hicolor/128x128/apps/codenomad-tauri.png": "icons/linux/128x128.png",
+          "/usr/share/icons/hicolor/256x256/apps/codenomad-tauri.png": "icons/linux/256x256.png",
+          "/usr/share/icons/hicolor/512x512/apps/codenomad-tauri.png": "icons/linux/512x512.png"
+        }
+      }
+    },
     "resources": [
       "resources/server",
       "resources/ui-loading"