feat: add password protection UI and fix launch flow

- Password management UI in settings (set/change/remove password)
- Shield icon on play button for protected identities
- Interactive password popup on launch with inline error display
- Fix: re-throw password errors instead of falling to local tokens
- Fix: password popup properly cleans up on success/cancel
- Fix: expose updatePasswordShieldIcon for cross-module access

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

preload.js

@@ -2,6 +2,7 @@ const { contextBridge, ipcRenderer } = require('electron');
 
 contextBridge.exposeInMainWorld('electronAPI', {
   launchGame: (playerName, javaPath, installPath, gpuPreference) => ipcRenderer.invoke('launch-game', playerName, javaPath, installPath, gpuPreference),
+  launchGameWithPassword: (playerName, javaPath, installPath, gpuPreference, password) => ipcRenderer.invoke('launch-game-with-password', playerName, javaPath, installPath, gpuPreference, password),
   installGame: (playerName, javaPath, installPath, branch) => ipcRenderer.invoke('install-game', playerName, javaPath, installPath, branch),
   closeWindow: () => ipcRenderer.invoke('window-close'),
   minimizeWindow: () => ipcRenderer.invoke('window-minimize'),
@@ -107,6 +108,15 @@ contextBridge.exposeInMainWorld('electronAPI', {
   deleteUuidForUser: (username) => ipcRenderer.invoke('delete-uuid-for-user', username),
   resetCurrentUserUuid: () => ipcRenderer.invoke('reset-current-user-uuid'),
 
+  // Password Management methods
+  checkPasswordStatus: (uuid) => ipcRenderer.invoke('check-password-status', uuid),
+  setPlayerPassword: (uuid, password, currentPassword) => ipcRenderer.invoke('set-player-password', uuid, password, currentPassword),
+  removePlayerPassword: (uuid, currentPassword) => ipcRenderer.invoke('remove-player-password', uuid, currentPassword),
+  promptPassword: () => ipcRenderer.invoke('prompt-password'),
+  onPasswordPrompt: (callback) => {
+    ipcRenderer.on('show-password-prompt', (event, data) => callback(data));
+  },
+
   // Java Wrapper Config API
   loadWrapperConfig: () => ipcRenderer.invoke('load-wrapper-config'),
   saveWrapperConfig: (config) => ipcRenderer.invoke('save-wrapper-config', config),