fix: save agent prompt and reload changes reliably

Agent settings now correctly save an emptied system prompt instead of silently keeping the old text.

After saving agent, command, or skill settings, OpenChamber refreshes the updated configuration instead of showing stale values from a short-lived cache.

Reload actions now surface refresh failures consistently while avoiding noisy background errors.

packages/vscode/webview/main.tsx

@@ -1354,7 +1354,7 @@ onCommand('showSettings', () => {
 // and refreshes config/data. Triggered by the "Restart API Connection" command.
 onCommand('reloadOpenCode', () => {
   void import('@openchamber/ui/stores/useAgentsStore').then(({ reloadOpenCodeConfiguration }) => {
-    void reloadOpenCodeConfiguration();
+    void reloadOpenCodeConfiguration().catch(() => undefined);
   });
 });