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/main.ts

@@ -1,3 +1,6 @@
+import log from "electron-log/main";
+log.initialize();
+
 import path from "node:path";
 import { pathToFileURL } from "node:url";
 import { existsSync } from "node:fs";