feat(desktop): add file logging with electron-log

Logs from both main and renderer processes now persist to
~/Library/Logs/Paseo/main.log (macOS) with automatic rotation.
Removes the unused webview_log IPC handler.

packages/desktop/src/preload.ts

@@ -1,3 +1,4 @@
+import "electron-log/preload";
 import { contextBridge, ipcRenderer } from "electron";
 
 type EventHandler = (payload: unknown) => void;