Desktop: pressing Enter on empty input should not send/interrupt

Description

In the OpenCode desktop app (Windows), pressing the Enter key while the input field is empty sends the message. This becomes a problem when the agent is executing a task -- accidentally pressing Enter will interrupt the ongoing task.

Steps to reproduce

1. Start a conversation and ask the agent to perform a task
2. While the agent is executing, press Enter with the input field empty
3. The empty message is sent, which interrupts the current task

Expected behavior

When the input field is empty, pressing Enter should be a no-op. Messages should only be sent when there is actual content in the input field.

Additional context

The desktop prompt shortcuts are documented as "currently not configurable via opencode.json", so there is no workaround via configuration files. This needs to be fixed in the application logic itself.