refactor: remove bundled Claude Code binary support

- Remove all bundled/sidecar binary functionality
- Delete build scripts for fetching and building Claude executables
- Simplify binary detection to only support system installations
- Update UI to remove bundled installation options
- Update build configuration and documentation

src/components/Settings.tsx

@@ -429,7 +429,7 @@ export const Settings: React.FC<SettingsProps> = ({
                       <div>
                         <Label className="text-sm font-medium mb-2 block">Claude Code Installation</Label>
                         <p className="text-xs text-muted-foreground mb-4">
-                          Select which Claude Code installation to use. Bundled version is recommended for best compatibility.
+                          Select which Claude Code installation to use.
                         </p>
                       </div>
                       <ClaudeVersionSelector