Cap Scrypt fiat buy orders at 200k for CHF/EUR

[TaprootFreak]

Summary

• Limits individual Scrypt buy order size to 200,000 when the trade asset is CHF or EUR
• Remaining amounts are automatically processed in subsequent liquidity management cycles (rule check runs every minute)
• Only affects the buy command — sell and sell-if-deficit are unchanged

Test plan

• Verify buy orders with CHF/EUR > 200k are capped at 200k
• Verify buy orders with CHF/EUR <= 200k are unaffected
• Verify buy orders with other trade assets (e.g. USDT) are unaffected
• Verify remaining deficit is picked up in the next LM cycle