Extract shared utilities into workspace package (#5843)

## Summary

Extracts shared formatting and network utilities into dedicated
workspace package.

## Changes

- **What**: Created `@comfyorg/shared-frontend-utils` package containing
formatUtil and networkUtil
- **Breaking**: None - utilities remain accessible via path aliases in
`tsconfig`

Split `createAnnotatedPath` and `electronMirrorCheck` out and left in
frontend, due to their tightly-coupled nature. See [discussion on this
PR](https://github.com/Comfy-Org/ComfyUI_frontend/pull/5843#issuecomment-3344724727).

src/utils/electronMirrorCheck.ts

@@ -0,0 +1,13 @@
+import { electronAPI } from '@/utils/envUtil'
+import { isValidUrl } from '@/utils/formatUtil'
+
+/**
+ * Check if a mirror is reachable from the electron App.
+ * @param mirror - The mirror to check.
+ * @returns True if the mirror is reachable, false otherwise.
+ */
+export const checkMirrorReachable = async (mirror: string) => {
+  return (
+    isValidUrl(mirror) && (await electronAPI().NetWork.canAccessUrl(mirror))
+  )
+}