fix(launcher): guard hash_prefix_length select on native_device existence

native_device can be undefined during initial load (before device config
is fetched). The select bind:value was doing a hard property access that
threw a TypeError crash when native_device was null/undefined. Wrapped
in {#if $ae_loc.native_device} to defer rendering until it's available.

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

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

@@ -131,6 +131,7 @@
                     >
                     <div class="flex items-center justify-between px-1">
                         <span class="text-[9px]">Hash Prefix Length</span>
+                        {#if $ae_loc.native_device}
                             <select
                                 bind:value={
                                     $ae_loc.native_device.hash_prefix_length
@@ -141,6 +142,9 @@
                                 <option value={2}>2 chars</option>
                                 <option value={3}>3 chars</option>
                             </select>
+                        {:else}
+                            <span class="text-[9px] opacity-50 italic">loading…</span>
+                        {/if}
                     </div>
                     <p class="text-[8px] opacity-40 italic mt-1">
                         * Prefix change requires a full app reload to take