feat: polish theme tooling, diagnostics and launcher workflows

Expand the theme editor with multi-select, snapping, context menus, draft
recovery and export validation; add theme backups and trust prompts. Add
in-app diagnostics and rotating log bundle viewing, hardware-accelerated
theme video playback on macOS, and refresh the settings, setup wizard and
theme gallery layouts.

src/lib/components/theme/ThemeV2Background.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import { custom_theme_volume } from '$lib/global';
-  import { themeMediaSource } from '$lib/themeMedia';
+  import { themeMediaSource, themeVideoLifecycle } from '$lib/themeMedia';
   import type { ThemeV2Definition } from '$lib/themeV2';
   import { themeAssetUrl } from '$lib/themeV2';
   import { reduceAnimations } from '$lib/userSettings';
@@ -116,6 +116,7 @@
       <video
         class="absolute inset-0 h-full w-full object-cover"
         use:themeMediaSource={assetUrl(background.src)}
+        use:themeVideoLifecycle
         autoplay
         loop
         muted={background.muted !== false}