refactor(launcher): consolidate menu controls and anchor to bottom

- Combine Extend/Mirror into a single toggle button, moved behind edit_mode
- All edit-mode controls (All Files, All Sessions, Display) now share consistent preset-tonal-tertiary styling
- Remove the always-visible display row and its non-native-mode disclaimer
- Wrap Menu_launcher_controls in mt-auto to keep it pinned to the bottom of the sidebar regardless of session count
- Add min-w-20 to file size chip to prevent collapse on narrow sessions

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

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

@@ -247,5 +247,7 @@ let ae_promises: key_val = $state({
             bind:trigger_reload__event_session_obj_id />
     {/if}
 
-    <Menu_launcher_controls />
+    <div class="mt-auto w-full">
+        <Menu_launcher_controls />
+    </div>
 </div>