fix(proxy): resolve 404 error and auto-setup proxy targets

Issues fixed:
1. Route prefix mismatch - Live config was set to use /claude, /codex,
   /gemini prefixes but server only had routes without prefixes
2. Proxy targets not auto-configured - start_with_takeover only modified
   Live config but didn't set is_proxy_target=true for current providers

Changes:
- Add prefixed routes (/claude/v1/messages, /codex/v1/*, /gemini/v1beta/*)
  to server.rs for backward compatibility
- Remove URL prefixes from takeover_live_configs() - server can route
  by API endpoint path alone (/v1/messages=Claude, /v1/chat/completions=Codex)
- Add setup_proxy_targets() method that automatically sets current providers
  as proxy targets when starting proxy with takeover
- Unify proxy toggle in SettingsPage to use takeover mode (same as main UI)
- Fix error message extraction in useProxyStatus hooks
- Fix provider switch logic to check both takeover flag AND proxy running state

src/components/proxy/AutoFailoverConfigPanel.tsx

@@ -18,8 +18,11 @@ export interface AutoFailoverConfigPanelProps {
 
 export function AutoFailoverConfigPanel({
   enabled,
-  onEnabledChange,
+  onEnabledChange: _onEnabledChange,
 }: AutoFailoverConfigPanelProps) {
+  // Note: onEnabledChange is currently unused but kept in the interface
+  // for potential future use by parent components
+  void _onEnabledChange;
   const { t } = useTranslation();
   const { data: config, isLoading, error } = useCircuitBreakerConfig();
   const updateConfig = useUpdateCircuitBreakerConfig();
@@ -262,7 +265,7 @@ export function AutoFailoverConfigPanel({
           </Button>
           <Button
             onClick={handleSave}
-            disabled={updateConfig.isPending || !formData.enabled}
+            disabled={updateConfig.isPending || !enabled}
           >
             {updateConfig.isPending ? (
               <>