feat: rename "notes" to "crumbs" throughout the UI

Replace all user-facing "note(s)" with "crumb(s)" — sidebar, search
placeholder, editor placeholders, empty states. Use Lucide icons
(StickyNote, Archive, Trash2, Tag) in sidebar for consistency.

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

src/lib/components/SearchBar.svelte

@@ -43,7 +43,7 @@
 		</svg>
 		<input
 			type="text"
-			placeholder="Search notes..."
+			placeholder="Search crumbs..."
 			bind:value={query}
 			oninput={handleSearch}
 			class="w-full bg-transparent text-sm text-gray-800 outline-none placeholder:text-gray-500"