fix: market expiry guard, FAK orders, 2% slippage, sanitize CLOB logs

Market expiry guard (executor.js):
- getMarketOptions() now returns endDateIso, active, acceptingOrders
  from Gamma API response
- executeBuy() skips immediately if market is closed / not accepting orders
- executeBuy() skips if market closes within MIN_MARKET_TIME_LEFT seconds
  (default 300 s = 5 min), logging exact time remaining
- Add MIN_MARKET_TIME_LEFT to config and .env.example

FAK + 2% slippage (executor.js):
- Replace OrderType.FOK with OrderType.FAK for both BUY and SELL
  market orders — eliminates "FOK fully filled or killed" failures
- Reduce slippage from 5% to 2% (price * 1.02 / price * 0.98)
- Fix zero-fill detection: FAK success with 0 shares logs "no liquidity"
  and retries instead of recording a phantom fill

CLOB log sanitization (logger.js + index.js):
- Add sanitizeClobMessage(): strips axios config object (auth headers)
  from [CLOB Client] dumps, keeps only HTTP status + error string
- Add interceptConsole(): overrides console.error/warn globally
- Call interceptConsole() at startup in index.js

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/config/index.js

@@ -46,6 +46,9 @@ const config = {
   maxRetries: 5,
   retryDelay: 3000,
 
+  // Skip buy if market closes within this many seconds (default 5 minutes)
+  minMarketTimeLeft: parseInt(process.env.MIN_MARKET_TIME_LEFT || '300', 10),
+
   // ── Market Maker ──────────────────────────────────────────────
   mmAssets:        (process.env.MM_ASSETS || 'btc')
                      .split(',').map((s) => s.trim().toLowerCase()).filter(Boolean),