Send long Discord replies without truncation

[1cbyc]

What & why

Discord replies longer than 2,000 characters were sent once and silently truncated by the low-level sender. Split replies at 1,900 characters before sending so every character reaches the channel in order while short replies keep the existing single-send path.

Closes #53.

Testing

• python3 -m pytest tests/test_reply_channels.py -q (13 passed)
• python3 -m compileall -q taskuary/outbound.py tests/test_reply_channels.py
• Full offline suite reached 5,285 passes and 5 skips; remaining failures were caused by unavailable optional dependencies and exhausted local disk, outside the changed reply path.

Checklist

• Focused offline tests pass
• New behavior has a test
• No UI files touched
• Existing user-facing channel contract is unchanged; the truncation bug is removed

Co-authored-by: insisong emmanuelisaacnsisong@gmail.com