Change cooldown unit from seconds to minutes

- Updated minTimeBetweenTrades config to use minutes instead of seconds
- Changed default from 600 seconds to 10 minutes
- Updated Settings UI label from 'seconds' to 'minutes' and adjusted range (0-60 min)
- Updated .env comments to reflect new unit
- No functional change since cooldown enforcement not yet implemented (TODO in check-risk route)

app/settings/page.tsx

@@ -385,12 +385,12 @@ export default function SettingsPage() {
               description="Maximum number of trades allowed per hour."
             />
             <Setting
-              label="Cooldown Between Trades (seconds)"
+              label="Cooldown Between Trades (minutes)"
               value={settings.MIN_TIME_BETWEEN_TRADES}
               onChange={(v) => updateSetting('MIN_TIME_BETWEEN_TRADES', v)}
               min={0}
-              max={3600}
-              step={60}
+              max={60}
+              step={1}
               description="Minimum wait time between trades to prevent overtrading."
             />
           </Section>