Add a settings page for profit display and default stack

- Per-device toggle to hide your own net and the net ranking at tables
- Default starting stack set in settings; creating a table saves the
  stack, SB and BB used as the next defaults
- Number fields on create and settings select all on focus

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

public/assets/style.css

@@ -468,6 +468,9 @@ a {
 .tone-purple {
   background: linear-gradient(180deg, #c86ff0, #9440c2);
 }
+.tone-gray {
+  background: linear-gradient(180deg, #a1a1a8, #75757c);
+}
 
 /* セルの中の入力（ラベルが左、値が右） */
 .field-cell {