Replace threshold placeholder link with a real settings panel

Adds a "Loss thresholds" panel to the popup backed by the backend's
new GET/PATCH /me/settings endpoints, converting between the wire's
fractional percentages and whole-number form inputs only at that
boundary.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01RTorFQXMR9ZQtCKcMTXLHp

src/entrypoints/background.ts

@@ -7,8 +7,9 @@ import {
   requestWalletDisconnect,
   requestWalletReconnect,
 } from '@/background/wallet-auth';
+import { getSettings, updateSettings } from '@/background/settings-client';
 import { connectWsClient } from '@/background/ws-client';
-import type { NexaMessage } from '@/shared/messaging';
+import type { NexaMessage, SettingsResult } from '@/shared/messaging';
 
 export default defineBackground(() => {
   const ws = connectWsClient({
@@ -71,6 +72,18 @@ export default defineBackground(() => {
         void requestAccountSwitch();
         return false;
 
+      case 'nexa:get-settings':
+        getSettings()
+          .then((settings) => sendResponse({ settings } satisfies SettingsResult))
+          .catch((err) => sendResponse({ error: String(err) } satisfies SettingsResult));
+        return true; // keep the message channel open for the async response
+
+      case 'nexa:update-settings':
+        updateSettings(message.settings)
+          .then((settings) => sendResponse({ settings } satisfies SettingsResult))
+          .catch((err) => sendResponse({ error: String(err) } satisfies SettingsResult));
+        return true;
+
       default:
         return undefined;
     }