feat: add VPM update notification

[yuki-maruyama]

Summary

• Add an editor update checker that calls https://vpm.32ba.net/api/packages/<package>/latest/version
• Show an update dialog when a newer VPM version is available
• Add Unity .meta files with unique GUIDs for all new assets

Verification

• Verified every target package ID returns the expected latest version from the VPM API with curl
• Verified every added .cs file has a matching .meta file
• Verified generated Unity GUIDs are unique across the checked repositories
• Verified no manual update-check menu item remains in the added update notification code

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Handle AsyncOperation yields in editor coroutine runner

EditorCoroutine.Update only pauses for yielded values that implement IEnumerator, but GetLatestVersionCoroutine yields request.SendWebRequest() (a UnityWebRequestAsyncOperation). Because that yield is ignored, _routine.MoveNext() runs again on the next editor tick before the request completes, so request.result is often still InProgress and the code reports a failed update check even when the network call would succeed. This makes automatic/manual update checks unreliable in normal latency conditions.

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