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/Cargo.lock

@@ -3118,7 +3118,7 @@ dependencies = [
 
 [[package]]
 name = "psysonic"
-version = "1.3.0"
+version = "1.4.2"
 dependencies = [
  "reqwest 0.12.28",
  "rodio",

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "psysonic"
-version = "1.4.2"
+version = "1.4.4"
 description = "Psysonic Desktop Music Player"
 authors = []
 license = ""

src-tauri/gen/schemas/capabilities.json

@@ -1 +1 @@
-{"default":{"identifier":"default","description":"Default capabilities for Psysonic","local":true,"windows":["main"],"permissions":["core:default","shell:default","shell:allow-open","notification:default","global-shortcut:allow-register","global-shortcut:allow-unregister","store:default","store:allow-load","store:allow-set","store:allow-get","store:allow-save","dialog:default","dialog:allow-open","fs:default","fs:allow-write-file","fs:allow-mkdir","fs:scope-download-recursive","core:window:allow-set-title","core:window:allow-close","core:window:allow-hide","core:window:allow-show","core:window:allow-set-fullscreen","core:window:allow-is-fullscreen","core:window:allow-create","core:webview:allow-create-webview-window"],"platforms":["linux","macOS","windows"]}}
+{"default":{"identifier":"default","description":"Default capabilities for Psysonic","local":true,"windows":["main"],"permissions":["core:default","shell:default",{"identifier":"shell:allow-open","allow":[{"url":"https://**"}]},"notification:default","global-shortcut:allow-register","global-shortcut:allow-unregister","store:default","store:allow-load","store:allow-set","store:allow-get","store:allow-save","dialog:default","dialog:allow-open","fs:default","fs:allow-write-file","fs:allow-mkdir","fs:scope-download-recursive","core:window:allow-set-title","core:window:allow-close","core:window:allow-hide","core:window:allow-show","core:window:allow-set-fullscreen","core:window:allow-is-fullscreen","core:window:allow-create","core:webview:allow-create-webview-window"],"platforms":["linux","macOS","windows"]}}

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",