fix: resolve all 40 Svelte dev warnings for clean startup

- Add $state() to 4 reactive variables (guestMode, emailInput, passwordInput, searchInputElement)
- Replace 3 deprecated <svelte:component> with direct component references
- Fix 8 a11y issues: add ARIA roles, tabindex, keyboard handlers to click-handler divs
- Remove 22 unused CSS selectors across 8 shared-ui components

Zero warnings on dev startup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-ui/src/context-menu/ContextMenu.svelte

@@ -86,7 +86,6 @@
 
 {#if visible}
 	<!-- Backdrop to block clicks on elements behind -->
-	<!-- svelte-ignore a11y_no_static_element_interactions -->
 	<div
 		class="context-menu-backdrop"
 		onpointerdown={(e) => {
@@ -104,6 +103,11 @@
 			e.stopPropagation();
 			onClose();
 		}}
+		onkeydown={(e) => {
+			if (e.key === 'Escape') onClose();
+		}}
+		role="presentation"
+		tabindex="-1"
 	></div>
 
 	<!-- svelte-ignore a11y_no_noninteractive_element_interactions -->