add lk console command with PortAudio + WebRTC AEC

[theomonnom]

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In general, the fix is to ensure that the size used in the allocation (4 + len(data)) cannot overflow the int type and is within an acceptable bound. This means validating len(data) before performing the addition and before allocating the buffer.

The best way to fix this here, without changing existing functionality, is:

1. Reuse the existing maxMessageSize bound (1MB) to constrain the size of serialized messages on the write side as well as the read side. This keeps the IPC protocol symmetric: you cannot send larger messages than you are willing to receive.
2. In WriteProto, after proto.Marshal(msg) succeeds, check len(data):
   • If len(data) > maxMessageSize, return an error like ipc: message too large: %d bytes.
   • This implies 4 + len(data) is at most 4 + maxMessageSize, which is safely within int limits on all supported Go architectures and also below math.MaxUint32, consistent with the 4‑byte length prefix.
3. Because the bound is small (1MB), we do not need additional explicit overflow arithmetic guards; the inequality check is sufficient to guarantee that 4 + len(data) cannot overflow.

Concretely, in pkg/ipc/ipc.go, in WriteProto between lines 17–22, insert a size check on len(data) before computing buf := make([]byte, 4+len(data)). No new imports or helper functions are required.