fix: Correct MIN_QUALITY_SCORE to MIN_SIGNAL_QUALITY_SCORE

Settings UI was using wrong variable name (MIN_QUALITY_SCORE) while
code reads MIN_SIGNAL_QUALITY_SCORE. This caused quality score changes
in settings UI to have no effect.

Fixed:
- Settings API now reads/writes MIN_SIGNAL_QUALITY_SCORE
- Updated .env file to use correct variable name
- User's quality score increase to 81 will now work

Related: User increased min quality from 60 to 81 to filter out
small chop trades (avoiding -$99 trade with quality score 80).

app/api/settings/route.ts

@@ -119,7 +119,7 @@ export async function GET() {
       MAX_DAILY_DRAWDOWN: parseFloat(env.MAX_DAILY_DRAWDOWN || '-50'),
       MAX_TRADES_PER_HOUR: parseInt(env.MAX_TRADES_PER_HOUR || '6'),
       MIN_TIME_BETWEEN_TRADES: parseInt(env.MIN_TIME_BETWEEN_TRADES || '600'),
-      MIN_QUALITY_SCORE: parseInt(env.MIN_QUALITY_SCORE || '60'),
+      MIN_SIGNAL_QUALITY_SCORE: parseInt(env.MIN_SIGNAL_QUALITY_SCORE || '60'),
       SLIPPAGE_TOLERANCE: parseFloat(env.SLIPPAGE_TOLERANCE || '1.0'),
       DRY_RUN: env.DRY_RUN === 'true',
     }