feat: 趋势过滤信号记录系统 + 实时涨跌方向判断

- 新增 TrendFilter 信号记录（enter/exit），按完整信号和高分信号两档分类
- 信号持久化到 data/trend_signals_cache.json，开机自动恢复
- 新增 /api/trend-signals API + SSE trend_signal 实时广播
- 前端新增完整信号卡片和高分信号卡片，移除旧趋势检测卡片
- 评分加入 1h 涨跌方向和实时 drift 惩罚，下跌币不触发信号
- OKX 交易所支持（累积变动、动量、趋势检测）
- 修复 trend_filter.go 编译错误

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

db/db.go

@@ -150,6 +150,24 @@ func (d *DB) migrate() error {
 	);
 	CREATE INDEX IF NOT EXISTS idx_cm_events_coin   ON cm_events(coin);
 	CREATE INDEX IF NOT EXISTS idx_cm_events_created ON cm_events(created_at);
+
+	CREATE TABLE IF NOT EXISTS trend_signals (
+		id           INTEGER PRIMARY KEY AUTOINCREMENT,
+		coin         TEXT NOT NULL,
+		type         TEXT NOT NULL,
+		signal_score REAL,
+		price        REAL,
+		ema_52       REAL,
+		ema_slope    REAL,
+		volume_ratio REAL,
+		range_24h    REAL,
+		vol_baseline REAL,
+		price_above_ema INTEGER,
+		state        TEXT,
+		created_at   DATETIME NOT NULL
+	);
+	CREATE INDEX IF NOT EXISTS idx_trend_signals_coin ON trend_signals(coin);
+	CREATE INDEX IF NOT EXISTS idx_trend_signals_created ON trend_signals(created_at);
 	`
 	_, err := d.Exec(schema)
 	if err != nil {