feat: add velocity entry, fast-poll thread, tighten BEAR threshold

- Add velocity-based entry signal in strategy.py (VELOCITY_THRESHOLD=0.10,
  VELOCITY_MIN_MOVE=0.5%, VELOCITY_MIN_AGE_M=5)
- Add fast-poll thread in daemon/runner.py (SIGNAL_POLL_INTERVAL=15s)
  for sub-minute velocity event detection
- Add vol_ratio tiered condition and get_active_signals() to strategy.py
- Change BEAR_THRESHOLD -1.0 → -0.5 in market_regime.py to catch
  slow downtrends earlier (weighted 2h score)
- Expand sell_reason VARCHAR2(500) in price_db.py DDL
- Add velocity_backtest.py and sim10m.py for strategy experimentation
- Update STRATEGY.md: correct regime algorithm description (weighted 2h
  score, not BTC 1h ±5%), add fast-poll/velocity sections, add backtest
  section D, add change history table

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

core/market_regime.py

@@ -26,7 +26,7 @@ LEADERS: dict[str, float] = {
 TREND_HOURS = 2  # 2h 추세 기준
 
 BULL_THRESHOLD =  1.5   # score ≥ 1.5% → Bull
-BEAR_THRESHOLD = -1.0   # score <  -1.0% → Bear
+BEAR_THRESHOLD = -0.5   # score <  -0.5% → Bear
 
 # 레짐별 매수 조건 파라미터
 REGIME_PARAMS: dict[str, dict] = {