style(select): make dropdown menu more compact to match sm-size trigger

- Menu padding: 8px → 6px
- Menu gap: 6px → 4px
- Item min-height: var(--ui-height-sm) → calc(var(--ui-height-sm) - 4px)
- Item padding: 0.5rem 0.75rem → 0.375rem 0.5rem

web/src/index.css

@@ -394,14 +394,14 @@ pre,
 .ui-select-menu {
   display: flex;
   flex-direction: column;
-  gap: 6px;
+  gap: 4px;
   max-height: 280px;
   overflow: auto;
   border-radius: var(--radius-md);
   border: 1px solid var(--border);
   background: var(--bg-secondary);
   box-shadow: var(--shadow-md);
-  padding: 8px;
+  padding: 6px;
 }
 
 .ui-select-item {
@@ -416,8 +416,8 @@ pre,
   cursor: pointer;
   font-size: var(--ui-font-sm);
   line-height: 1.35;
-  min-height: var(--ui-height-sm);
-  padding: 0.5rem 0.75rem;
+  min-height: calc(var(--ui-height-sm) - 4px);
+  padding: 0.375rem 0.5rem;
   text-align: left;
 }