Switch Linux packaging from AppImage to deb + rpm + PKGBUILD

AppImage library bundling causes cascading compatibility failures on
rolling-release distros (Arch, mesa 26+): libwayland-egl conflicts
break EGL, removing it cascades into GLib version mismatches, and so
on. Native packages sidestep this entirely.

- tauri.conf.json: targets now ["deb","rpm","nsis","msi","dmg","updater"]
  — no AppImage
- release.yml: drop LINUXDEPLOY_EXCLUDELIST workaround (no longer needed);
  update install instructions in release body
- PKGBUILD: added for Arch/Manjaro users; builds from source via git tag;
  desktop entry sets WEBKIT_DISABLE_DMABUF_RENDERER=1 (required on Wayland)
- README: install table updated with distro-specific commands

Arch users: build from source with PKGBUILD or `npm run tauri build`.
Ubuntu/Debian/Fedora/openSUSE: install the .deb or .rpm from Releases.

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

src-tauri/tauri.conf.json

@@ -25,7 +25,7 @@
   },
   "bundle": {
     "active": true,
-    "targets": "all",
+    "targets": ["deb", "rpm", "nsis", "msi", "dmg", "updater"],
     "icon": [
       "icons/32x32.png",
       "icons/128x128.png",