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

src/routes/events/[event_id]/sign_in_out.svelte

@@ -184,8 +184,7 @@
 
 <span>
     {#if $events_loc.auth__person?.id}
-        <button
-            type="button"
+        <button type="button"
             class="btn btn-sm preset-tonal-warning"
             onclick={() => {
                 sign_out();
@@ -219,7 +218,7 @@
                     value={$events_sess.auth__entered_passcode ?? ''}
                     oninput={(e) => ($events_sess.auth__entered_passcode = e.target?.value)}
                 />
-                <button
+                <button type="button"
                     class="btn btn-md preset-tonal-primary border border-primary-500"
                     onclick={() => {
                         console.log('Sign in with URL values');
@@ -262,8 +261,7 @@
             </div>
 
             <!-- {#if $events_loc.auth__person?.id}
-        <button
-            type="button"
+        <button type="button"
             class="btn btn-sm variant-soft-warning"
             on:click={() => {
                 sign_out();