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-auth-ui/src/components/GuestWelcomeModal.svelte

@@ -238,10 +238,12 @@
 
 {#if visible && appInfo}
 	<!-- Modal Backdrop -->
-	<!-- svelte-ignore a11y_no_noninteractive_element_interactions -->
 	<div
 		class="modal-backdrop"
 		onclick={handleBackdropClick}
+		onkeydown={(e) => {
+			if (e.key === 'Escape') handleBackdropClick();
+		}}
 		role="dialog"
 		aria-modal="true"
 		aria-labelledby="welcome-title"