perf(frontend): lazy-load heavy components to shrink initial bundle

Defer loading components that are off the initial render path until they
are first needed, keeping them out of the bundle that loads on page entry.

- Add `lazyComponent` composable: a tiny rune-based holder that dynamic-
  imports a component on first `load()` and exposes it for `{@const}`
  rendering, with the component type inferred from the module so prop/
  binding type-checking stays intact.
- CommandPalette: loaded on the first Cmd/Ctrl+K and mounted open via a
  new `autoOpen` prop. It was previously imported by AppShell, i.e. in the
  initial chunk of every authenticated route (~27 KB). AppShell now owns
  the shortcut that triggers the load.
- FileViewer + WopiEditor: loaded when a preview/editor first opens, across
  files, recent, favorites and shared-with-me.
- PhotoLightbox / PlacesMap / PeopleView: loaded on first lightbox open or
  when the places/people tab is selected (the latter also defers maplibre).

Once loaded a component stays mounted and behaves exactly as before, so
behavior is unchanged on the second use onward.

frontend/src/lib/components/AppShell.svelte

@@ -6,7 +6,7 @@
 	import { searchFiles } from '$lib/api/endpoints/search';
 	import { fileInlineUrl } from '$lib/api/endpoints/files';
 	import type { FileItem, FolderItem } from '$lib/api/types';
-	import CommandPalette from '$lib/components/CommandPalette.svelte';
+	import { lazyComponent } from '$lib/composables/lazyComponent.svelte';
 	import Icon from '$lib/icons/Icon.svelte';
 	import { iconNameFromClass } from '$lib/utils/display';
 	import { userInitials, avatarColorIndex } from '$lib/utils/avatar';
@@ -19,6 +19,10 @@
 
 	let { children }: { children: Snippet } = $props();
 
+	// The command palette is loaded on its first Cmd/Ctrl+K and mounted open.
+	// Until then its ~400-line module stays out of the initial bundle.
+	const palette = lazyComponent(() => import('$lib/components/CommandPalette.svelte'));
+
 	interface NavLink {
 		href: string;
 		label: string;
@@ -224,6 +228,13 @@
 <svelte:window
 	onclick={closeMenus}
 	onkeydown={(e) => {
+		// First Cmd/Ctrl+K loads the palette and mounts it open; once mounted,
+		// the palette's own handler takes over toggling/closing.
+		if ((e.metaKey || e.ctrlKey) && e.key.toLowerCase() === 'k' && !palette.component) {
+			e.preventDefault();
+			void palette.load();
+			return;
+		}
 		if (e.key !== 'Escape') return;
 		if (aboutOpen) aboutOpen = false;
 		else if (searchActive) closeMobileSearch();
@@ -683,7 +694,10 @@
 	</div>
 {/if}
 
-<CommandPalette />
+{#if palette.component}
+	{@const CommandPalette = palette.component}
+	<CommandPalette autoOpen />
+{/if}
 
 <style>
 	/* Body becomes the sidebar+main flex row only while the shell is mounted. */