Introduce per-route send queues and dedicated sender tasks so terminal output
does not await slow WebSocket clients. Output is buffered up to a bounded
queue; when full, the oldest data is dropped to keep sessions responsive.
Sender tasks enforce a send timeout and close slow/broken sockets, preventing
terminal run loops from stalling indefinitely.
Tests updated/added to verify:
- queued output instead of direct ws.send_bytes
- sender timeout closes sockets
- queue overflow drops oldest
- session close stops sender task
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