refactor(ui): standardize button types and migrate file operations to V3 Action API

src/routes/events/[event_id]/(launcher)/launcher_background_sync.svelte

@@ -248,7 +248,7 @@
         <div class="bg-black/90 text-white p-3 rounded-lg border border-primary-500 shadow-2xl text-[10px] font-mono min-w-48 pointer-events-auto">
             <div class="flex justify-between border-b border-primary-500 pb-1 mb-2">
                 <span class="font-bold text-primary-400">NATIVE SYNC MONITOR</span>
-                <button onclick={() => show_monitor = false} class="text-error-500 hover:text-error-400">×</button>
+                <button type="button" onclick={() => show_monitor = false} class="text-error-500 hover:text-error-400">×</button>
             </div>
 
             <div class="grid grid-cols-2 gap-x-4 gap-y-1 mb-2">
@@ -286,7 +286,7 @@
     {/if}
 
     {#if currently_syncing}
-        <button
+        <button type="button"
             onclick={() => show_monitor = !show_monitor}
             class="bg-black/80 text-white p-2 rounded-lg text-[10px] border border-primary-500 animate-pulse shadow-2xl pointer-events-auto transition-transform active:scale-95"
         >
@@ -301,7 +301,7 @@
         </button>
     {:else}
         <!-- Secret button area to toggle monitor when not syncing -->
-        <button
+        <button type="button"
             onclick={() => show_monitor = !show_monitor}
             class="w-8 h-8 opacity-0 hover:opacity-20 bg-primary-500 rounded-full pointer-events-auto flex items-center justify-center transition-opacity"
             title="Toggle Sync Monitor"