Fix missing await on response.json() in sendViaKey error path

[Copilot]

sendViaKey passed an unresolved Promise to parseError instead of the awaited JSON body, causing every non-200 error response to surface as "Unknown {}" rather than the actual server message.

// before
if (response.status !== 200) return parseError(response.json());

// after
if (response.status !== 200) return parseError(await response.json());

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