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-tauri/src/lib.rs

@@ -648,11 +648,15 @@ pub fn run() {
             commands::get_auto_launch_status,
             // Proxy server management
             commands::start_proxy_server,
+            commands::start_proxy_with_takeover,
             commands::stop_proxy_server,
+            commands::stop_proxy_with_restore,
             commands::get_proxy_status,
             commands::get_proxy_config,
             commands::update_proxy_config,
             commands::is_proxy_running,
+            commands::is_live_takeover_active,
+            commands::switch_proxy_provider,
             // Proxy failover commands
             commands::get_proxy_targets,
             commands::set_proxy_target,