feat: new app icon, AUR package, remove AppImage (v1.4.4)

- New app icon across all platforms
- AUR package: Arch/CachyOS users can install via yay/paru
- AppImage removed: incompatible with non-Ubuntu distros due to
  bundled WebKitGTK vs system Mesa/EGL conflicts
- CI: build only deb+rpm for Linux, drop GStreamer/linuxdeploy deps

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Psysonic",
-  "version": "1.4.3",
+  "version": "1.4.4",
   "identifier": "dev.psysonic.app",
   "build": {
     "beforeDevCommand": "npm run dev",