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>

apps/manacore/apps/web/src/lib/components/onboarding/steps/ProfileStep.svelte

@@ -146,7 +146,7 @@
 
 		<!-- Email (readonly) -->
 		<div>
-			<label class="block text-sm font-medium mb-2 text-muted-foreground">E-Mail</label>
+			<p class="block text-sm font-medium mb-2 text-muted-foreground">E-Mail</p>
 			<div class="px-4 py-3 border rounded-xl bg-muted text-muted-foreground">
 				{authStore.user?.email || 'Nicht verfügbar'}
 			</div>

apps/manacore/apps/web/src/routes/(app)/+layout.svelte

@@ -229,7 +229,7 @@
 	}
 
 	// ── Guest Mode ──────────────────────────────────────────
-	let guestMode: GuestMode | null = null;
+	let guestMode = $state<GuestMode | null>(null);
 
 	// ── Onboarding ──────────────────────────────────────────
 	function handleOnboardingComplete() {