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/shared/messaging.ts

@@ -1,4 +1,4 @@
-import type { ConnectionStatus, LockState } from './types';
+import type { ConnectionStatus, LockState, ThresholdSettings } from './types';
 
 /** browser.storage.local key backing the lock state seam in the background script. */
 export const LOCK_STATE_STORAGE_KEY = 'nexa:lockState';
@@ -28,7 +28,14 @@ export type NexaMessage =
   | { type: 'nexa:switch-account-request' }
   // Sign-out / switch account (popup -> background). See entrypoints/popup/App.tsx.
   | { type: 'nexa:sign-out' }
-  | { type: 'nexa:switch-account' };
+  | { type: 'nexa:switch-account' }
+  // Loss-threshold settings (popup -> background -> GET/PATCH /me/settings).
+  // See background/settings-client.ts and entrypoints/popup/App.tsx.
+  | { type: 'nexa:get-settings' }
+  | { type: 'nexa:update-settings'; settings: Partial<ThresholdSettings> };
+
+/** Response shape for 'nexa:get-settings'/'nexa:update-settings', returned via sendResponse. */
+export type SettingsResult = { settings: ThresholdSettings } | { error: string };
 
 /** Response shape for 'nexa:wallet-sign-request', returned via sendResponse (not a dispatched NexaMessage). */
 export type WalletSignResult = { signature: string } | { error: string };