feat(library): reindex button, live grid, archive-reappear fix, bigger carets

- Add one-click "reindex new files" button to the Library sidebar header
  (RefreshCw, calls startIndex rescan:false), spins + disables while active.
- Refresh the photos grid from the indexer WS stream (throttled during the
  scan + once on completion) so newly indexed files appear live.
- Fix archived photos flashing back into the grid when archiving others:
  drop the per-action settle-driven clearRemoved and reconcile removedIds
  against the actual cache instead (clears an id only once it's gone from
  the deduped pages). Covers archive, delete, and bulk-bar removals.
- Replace the tiny Unicode caret triangles with a 16px Lucide ChevronRight
  that rotates 90deg on expand, across folder tree rows, root, Tags, Review.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/lib/components/layout/FolderTree.svelte

@@ -41,7 +41,7 @@
 	import { filters } from '$lib/stores/filters.svelte';
 	import { browser } from '$app/environment';
 	import { untrack } from 'svelte';
-	import { FolderInput, FolderPlus, Pencil, Trash2 } from 'lucide-svelte';
+	import { ChevronRight, FolderInput, FolderPlus, Pencil, Trash2 } from 'lucide-svelte';
 	import Self from './FolderTree.svelte';
 	import KebabMenu, { Item, Separator } from './KebabMenu.svelte';
 
@@ -164,19 +164,21 @@
 			>
 				{#if hasChildren}
 					<button
-						class="flex h-[18px] w-4 items-center justify-center text-[10px]"
+						class="flex h-[18px] w-5 items-center justify-center rounded hover:text-foreground"
 						class:text-muted-foreground={!active}
 						onclick={() => toggle(node.path)}
 						title={open ? 'Collapse' : 'Expand'}
 						aria-label={open ? 'Collapse' : 'Expand'}
 					>
-						{open ? '▾' : '▸'}
+						<ChevronRight
+							class="h-4 w-4 transition-transform duration-150 {open ? 'rotate-90' : ''}"
+						/>
 					</button>
 				{:else}
 					<!-- Spacer keeps childless siblings aligned with their chevroned
 					     peers at every depth, so labels share a common left edge
 					     across the sidebar (folders, heaps, views, manage). -->
-					<span class="inline-block h-[18px] w-4" aria-hidden="true"></span>
+					<span class="inline-block h-[18px] w-5" aria-hidden="true"></span>
 				{/if}
 				<!--
 					Count badge lives INSIDE the button so the entire row (label