feat: migrate ERP configuration from .env to per-user database storage

- Moved ERP credentials (URL, username, password) from environment variables to dbo_BIPUsers table
- Each user now has their own ERP configuration stored in the database
- Added UserErpConfigService for managing per-user ERP settings
- Updated cleaner and extractor handlers to fetch ERP config from database instead of .env
- Removed ERP fields from ConfigManager UI editable fields
- Added new IPC handlers and preload APIs for user ERP config management
- Includes migration script to transfer existing .env ERP settings to database
- Added migration guide documentation

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/preload/index.ts

@@ -137,6 +137,16 @@ const api = {
       ipcRenderer.invoke('materialType:delete', { materialName, managerName }),
     upsertBatch: (request: MaterialTypeBatchRequest) =>
       ipcRenderer.invoke('materialType:upsertBatch', request)
+  },
+
+  // User ERP Configuration service
+  userErpConfig: {
+    getCurrent: () => ipcRenderer.invoke('user-erp-config:getCurrent'),
+    update: (config: { url: string; username: string; password: string }) =>
+      ipcRenderer.invoke('user-erp-config:update', config),
+    testConnection: (config: { url: string; username: string; password: string }) =>
+      ipcRenderer.invoke('user-erp-config:testConnection', config),
+    getAll: () => ipcRenderer.invoke('user-erp-config:getAll')
   }
 } as const