feat: add full-margin position sizing mode across four exchanges

Env POSITION_SIZING_MODE switches risk vs full-margin (available*buffer, BTC/ETH 10x). Blocks trend/roll/key auto opens in full margin, purges breakout/fib monitors with WeChat notice, keeps RR check and initial SL snapshot for records.

Co-authored-by: Cursor <cursoragent@cursor.com>

strategy_trend_register.py

@@ -106,6 +106,15 @@ def _row(cfg, row) -> dict:
 
 def precheck_trend_start(cfg: dict, conn) -> tuple[bool, str]:
     m = _m(cfg)
+    mode = getattr(m, "POSITION_SIZING_MODE", None) or "risk"
+    try:
+        from position_sizing_lib import OPEN_SOURCE_TREND, assert_open_source_allowed
+
+        ok_src, src_msg = assert_open_source_allowed(mode, OPEN_SOURCE_TREND)
+        if not ok_src:
+            return False, src_msg
+    except Exception:
+        pass
     now = m.app_now()
     if not m.trading_day_reset_allows_new_open(now):
         return False, f"北京时间 {cfg['reset_hour']}:00 前不允许持仓"