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/price_db.py

@@ -170,6 +170,13 @@ def ensure_trade_results_table() -> None:
             except oracledb.DatabaseError as e:
                 if e.args[0].code not in (955, 1408):
                     raise
+        # sell_reason 컬럼이 100 BYTE 이하이면 500으로 확장
+        try:
+            conn.cursor().execute(
+                "ALTER TABLE trade_results MODIFY sell_reason VARCHAR2(500)"
+            )
+        except oracledb.DatabaseError:
+            pass  # 이미 500 이상이거나 컬럼 없으면 무시
 
 
 def record_trade(