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/bottom-stack/NotificationBar.svelte

@@ -32,7 +32,8 @@
 			{#if active.action}
 				<button class="notification-action" onclick={active.action.onClick}>
 					{#if active.action.icon}
-						<svelte:component this={active.action.icon} size={14} weight="bold" />
+						{@const ActionIcon = active.action.icon}
+						<ActionIcon size={14} weight="bold" />
 					{/if}
 					{active.action.label}
 					<ArrowRight size={12} />