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_file_cont.svelte

@@ -765,7 +765,7 @@ function prevent_default<T extends Event>(fn: (event: T) => void) {
         </span>
 
         <span
-            class="event_file_size preset-filled-surface-100-900 flex w-22 max-w-28 flex-row items-center justify-end gap-1 rounded py-0.5 text-center text-xs"
+            class="event_file_size preset-filled-surface-100-900 flex min-w-20 w-22 max-w-28 flex-row items-center justify-end gap-1 rounded py-0.5 text-center text-xs"
             class:hidden={hide_size}>
             <Save size="0.85em" class="inline" />
             {#if event_file_obj.file_size}{ae_util.format_bytes(