Show equivalent contract leverage on options order panel.

Display notional-over-premium leverage at current index and at the user target price for quick sizing comparison.

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

lib/options/options_pricing_lib.py

@@ -257,3 +257,17 @@ def estimate_expiry_profit_at_index(
     else:
         return None
     return round((intrinsic - float(entry_px)) * float(eth_amount), 4)
+
+
+def equivalent_contract_leverage(
+    *,
+    index_px: float | None,
+    eth_amount: float | None,
+    total_premium: float | None,
+) -> float | None:
+    """名义价值 / 权利金，近似相当于永续合约杠杆倍数（测算用）。"""
+    if index_px is None or eth_amount is None or total_premium is None:
+        return None
+    if eth_amount <= 0 or total_premium <= 0:
+        return None
+    return round(float(index_px) * float(eth_amount) / float(total_premium), 1)