Add dual exit modes: fixed USDT or premium multiple.

Net PnL (after estimated close fees) drives auto close; Plan/Settings expose the choice.

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

frontend/src/styles/app.css

@@ -225,7 +225,8 @@ input {
   color: var(--muted);
 }
 
-.field input {
+.field input,
+.field select {
   background: var(--input);
   border: 1px solid var(--line);
   color: var(--text);
@@ -234,7 +235,8 @@ input {
   outline: none;
 }
 
-.field input:focus {
+.field input:focus,
+.field select:focus {
   border-color: rgba(240, 185, 11, 0.55);
 }