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/app.css

@@ -40,7 +40,6 @@
 	--font-size-2xl: 1.5rem;
 	
 	/* Layout */
-	--nav-height: 60px;
 	--content-max-width: 768px;
 	
 	/* Shadows */
@@ -67,7 +66,7 @@ html {
 body {
 	background-color: var(--bg-secondary);
 	color: var(--text-primary);
-	min-height: 100vh;
+	min-height: 100dvh;
 	overflow-x: hidden;
 }
 
@@ -113,11 +112,6 @@ a:hover {
 	padding: 0 var(--spacing-md);
 }
 
-.page {
-	min-height: calc(100vh - var(--nav-height));
-	padding-bottom: calc(var(--nav-height) + var(--spacing-md));
-}
-
 /* Utility Classes */
 .text-center {
 	text-align: center;
@@ -178,9 +172,3 @@ html {
 	scroll-behavior: smooth;
 }
 
-/* Safe Area Padding (for mobile notches) */
-@supports (padding: env(safe-area-inset-bottom)) {
-	.page {
-		padding-bottom: calc(var(--nav-height) + var(--spacing-md) + env(safe-area-inset-bottom));
-	}
-}