refactor(web): remove old routes and BottomNav for single-screen redesign

Delete /tasks/new, /tasks/[uuid], /projects, /tags routes and BottomNav
component. Simplify layout to slot-only with 100dvh flexbox. Remove
nav-height CSS variable and .page padding rules.

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

opal-web/src/routes/+layout.svelte

@@ -1,32 +1,16 @@
 <script>
 	import '../app.css';
-	import BottomNav from '$lib/components/BottomNav.svelte';
-	import { authStore } from '$lib/stores/auth.js';
-	import { page } from '$app/stores';
-	
-	// Check if on auth pages (don't show nav)
-	$: isAuthPage = $page.url.pathname.startsWith('/auth');
 </script>
 
 <div class="app">
-	<main class="main">
-		<slot />
-	</main>
-	
-	{#if $authStore.isAuthenticated && !isAuthPage}
-		<BottomNav />
-	{/if}
+	<slot />
 </div>
 
 <style>
 	.app {
-		min-height: 100vh;
+		height: 100dvh;
 		display: flex;
 		flex-direction: column;
-	}
-	
-	.main {
-		flex: 1;
-		width: 100%;
+		overflow: hidden;
 	}
 </style>