launcher: add font size cycler to footer bar

Onsite operators may have the sys menu locked/unavailable. This button
in the always-visible launcher footer gives them direct A / A+ / A−
control that cycles $ae_loc.font_size_mode, which the root layout DOM
effect picks up and applies as html.font-size-* class.

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

@@ -688,6 +688,28 @@
         {/if}
     </span>
 
+    <!-- Font size cycler: allows onsite operators to adjust text size without needing
+         access to the global sys menu, which may be unavailable in kiosk/locked setups. -->
+    <button
+        type="button"
+        onclick={() => {
+            const mode = $ae_loc.font_size_mode;
+            if (!mode || mode === 'default') $ae_loc.font_size_mode = 'larger';
+            else if (mode === 'larger') $ae_loc.font_size_mode = 'smaller';
+            else $ae_loc.font_size_mode = 'default';
+        }}
+        class="group px-2 py-0.5 rounded-md font-mono font-bold hover:bg-surface-500/10 transition-colors duration-200"
+        title="Font size: {$ae_loc.font_size_mode ?? 'default'} — tap to cycle (default → larger → smaller)"
+    >
+        {#if $ae_loc.font_size_mode === 'larger'}
+            <span>A+</span>
+        {:else if $ae_loc.font_size_mode === 'smaller'}
+            <span class="text-[0.7em]">A−</span>
+        {:else}
+            <span>A</span>
+        {/if}
+    </button>
+
     <div
         class="current_datetime font-mono px-2 hover:font-bold hover:bg-white dark:hover:bg-slate-700 transition-colors"
     >