phsl / new-api

Backend
• `model/channel.go`
  – On multi-key channel updates, recalculate `MultiKeySize` from the current key list.
  – If the request omits `key`, fetch existing keys from DB to avoid resetting the count to `0/0`.
  – Remove out-of-range entries from `MultiKeyStatusList` to keep data consistent.

Frontend
• `web/src/pages/Channel/EditChannel.js`
  – Vertex AI channels no longer require re-uploading a key file in edit mode.
  – When no new key is provided during editing, exclude the `key` field from the payload to prevent overwriting the stored value.

These changes ensure that editing a channel no longer zeroes out the enabled key counter and that Vertex AI channels can be modified without mandatory key re-submission.