feat: project tree delete, close tab, Linux AppImage bundling

- Right-click delete on classes in Project Tree dock
- File > Close (Ctrl+W) to unload active project tab
- File > Open now replaces current project instead of merging
- Linux CI builds AppImage via linuxdeploy + Qt plugin so users
  don't need Qt installed (fixes libQt6Core.so.6 not found)
- Pin ubuntu-22.04 for broader glibc compatibility

deploy/Reclass.desktop

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Type=Application
+Name=Reclass
+Comment=Memory structure reverse engineering tool
+Exec=Reclass
+Icon=reclass
+Categories=Development;Debugger;
+Terminal=false