feat: identity protection UI, duplicate guards, name-lock enforcement (v2.4.6)

- Add password set/change/remove with loading states and double-click prevention
- Add protected identity deletion flow (server-side password removal first)
- Add restore flow for password-protected UUIDs (verify password before saving)
- Add UUID duplicate checks in setUuidForUser (prevent accidental overwrites)
- Add name-locked error handling in launch flow (server enforces registered name)
- Sync shield icon across all identity mutation paths
- Refresh identity dropdown after all password/identity operations
- Propagate force flag through IPC for legitimate overwrites

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

preload.js

@@ -103,7 +103,7 @@ contextBridge.exposeInMainWorld('electronAPI', {
   // UUID Management methods
   getCurrentUuid: () => ipcRenderer.invoke('get-current-uuid'),
   getAllUuidMappings: () => ipcRenderer.invoke('get-all-uuid-mappings'),
-  setUuidForUser: (username, uuid) => ipcRenderer.invoke('set-uuid-for-user', username, uuid),
+  setUuidForUser: (username, uuid, force) => ipcRenderer.invoke('set-uuid-for-user', username, uuid, force),
   generateNewUuid: () => ipcRenderer.invoke('generate-new-uuid'),
   deleteUuidForUser: (username) => ipcRenderer.invoke('delete-uuid-for-user', username),
   resetCurrentUserUuid: () => ipcRenderer.invoke('reset-current-user-uuid'),