Increase sidebar left padding to pl-4 for safe focus ring clearance

pl-3 (12px) exactly matched the 8px outline + 4px offset with no buffer.
pl-4 (16px) matches pr-4 and gives 4px clearance to prevent subpixel
clipping of focus rings on left-column field type buttons.

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

app/javascript/template_builder/builder.vue

@@ -439,7 +439,7 @@
       <div
         v-if="withFieldsList && !isMobile"
         id="fields_list_container"
-        class="relative w-80 flex-none mt-1 pr-4 pl-3 hidden md:block fields-list-container"
+        class="relative w-80 flex-none mt-1 pr-4 pl-4 hidden md:block fields-list-container"
         :class="drawField || drawCustomField ? 'overflow-hidden' : 'overflow-y-auto overflow-x-hidden'"
       >
         <div