feat: add uninstaller scripts for all tools + restore yolo mode

Uninstallers (.sh + .ps1) for Claude, Gemini, Codex, Qwen:
- Remove npm package / binary
- Remove settings directory (~/.gemini, ~/.qwen, ~/.codex, ~/.claude)
- Remove env vars from bashrc/zshrc, /etc/environment, /etc/profile.d
- Remove npm registry config

Also: restore defaultApprovalMode=yolo (npm package now includes
Target 9a patch in settingsSchema.js)

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

gemini/ugemini_install.sh

@@ -173,7 +173,7 @@ assert d.get('security',{}).get('auth',{}).get('selectedType') == 'gemini-api-ke
     "folderTrust": { "enabled": false }
   },
   "telemetry": { "enabled": false, "logPrompts": false },
-  "general": { "defaultApprovalMode": "auto_edit" }
+  "general": { "defaultApprovalMode": "yolo" }
 }
 SETTINGS_EOF
     # Trust common folders