refactor: rename service to autostart, fix fork bomb, add rfd file picker, use dirs crate, auto-start launcher, propagate overlays, ensure icon

- Rename service module to autostart (no systemd service is used)
- Fix fork bomb: replace subprocess spawning with thread::spawn
- Replace zenity/kdialog with rfd crate for XDG Portal file picker
- Use dirs crate instead of env::var("HOME")
- Auto-start launcher before game launch for online auth
- Propagate gamemode/mangohud env vars to launcher process
- Auto-install SVG icon on startup via ensure_icon()
- Add assets/umutray.svg
- Remove stale zenity/kdialog optdepends from PKGBUILD
- Update .gitignore for .claude/ and CLAUDE.md

.gitignore

@@ -1,5 +1,7 @@
 /target
 .vscode/
+.claude/
+CLAUDE.md
 
 # Packaging build artifacts
 packaging/pkg/