feat: Short-Seite im Runner + Walk-Forward-CLI (--shorts Flag)

- BacktestConfig.allowShort: boolean (required, explizit)
- Runner: Short-Entry (stop = close + mult×ATR), updateChandelierShort für Trail,
  Stop-Check auf High >= stop, Gap-Fill nach oben
- Bestehende Runner-Tests: allowShort: false ergänzt (Verhalten byte-identisch)
- Neuer E2E-Test: Short-Breakout → trailing_stop; Long-Only-Sanity-Check
- walkforward.ts script: --shorts Flag, Ausgabe "Shorts: AN/AUS"
- walkforward.test.ts: allowShort: false ergänzt

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/server/scripts/walkforward.ts

@@ -19,7 +19,9 @@ for (const pair of PAIRS) {
   console.log(`${pair}: ${cov.count} Candles (${cov.from.toISOString()} → ${cov.to.toISOString()})`);
 }
 
-const baseCfg = { startCapital: 1000, risk: DEFAULT_RISK, exec: DEFAULT_EXEC, maxPositions: 4 };
+const allowShort = process.argv.includes('--shorts');
+const baseCfg = { startCapital: 1000, risk: DEFAULT_RISK, exec: DEFAULT_EXEC, maxPositions: 4, allowShort };
+console.log(`Shorts: ${allowShort ? 'AN' : 'AUS'}`);
 console.log(`\nWalk-Forward über ${((dataTo - dataFrom) / 86400000).toFixed(0)} Tage…\n`);
 
 const result = runWalkForward(candles15ByPair, baseCfg, dataFrom, dataTo, (msg) => console.log(msg));