Hide dialog weight/grams fields on event types that don't use them

The JS already sets .hidden per type, but 'dialog label { display: block }'
outranks the UA [hidden] rule, so the fields rendered anyway. Add the
explicit [hidden] override, matching the pattern used elsewhere in the file.

src/style.css

@@ -466,6 +466,9 @@ dialog::backdrop { background: rgba(0,0,0,0.4); }
 dialog h3 { margin: 0 0 12px; }
 
 dialog label { display: block; font-size: 0.85rem; color: var(--muted); margin-bottom: 10px; }
+/* The display rule above beats the UA [hidden] rule, so hide explicitly —
+   otherwise the weight/grams fields show on event types that don't use them. */
+dialog label[hidden] { display: none; }
 dialog label input, dialog label textarea { margin-top: 4px; }
 
 dialog menu {