fix: Auto-resize spell/class textareas on load; shrink delete column

- Add autoResize helper and wire it via ref callback (mount) and onInput
  (typing) to spell notes and class skills textareas
- Change .spell-del-col from width:40px to width:1px + white-space:nowrap
  so the delete button column shrink-wraps to its content

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

src/fabula-ultima-sheet.css

@@ -782,7 +782,8 @@ input[type="number"] {
 }
 
 .spell-del-col {
-  width: 40px;
+  width: 1px;
+  white-space: nowrap;
 }
 
 .spell-del-btn {