Reject zero/negative buy amount before sending transaction #2

Problem

pumpfun buy <mint> 0 sends a 0-lamport transaction to the network, wasting fees. Negative amounts are parsed as CLI flags (-1 → "No such option"), which is safe but confusing.

Fix

Add validation in src/pumpfun_cli/commands/trade.py buy(), after _validate_mint():

if sol_amount <= 0:
    error("Buy amount must be greater than zero.")

Files to change

• src/pumpfun_cli/commands/trade.py — add guard in buy()
• tests/test_commands/test_trade_cmd.py — add test for zero amount

How to test

uv run pytest tests/test_commands/test_trade_cmd.py -v