feat(mvp): phase 7 - UI polish & ambient backgrounds

Add layout system (sidebar, header, main layout), dark/light/system theme
with HSL customization, 3 ambient backgrounds (mesh gradient, particle field,
aurora), Cmd/Ctrl+K search dialog, page transitions, card hover effects,
status pulse animations, skeleton loaders, and responsive design. Polish
all existing pages with consistent theming.

src/routes/boards/[boardId]/+page.svelte

@@ -7,17 +7,19 @@
 </script>
 
 <svelte:head>
-	<title>{data.board.name}</title>
+	<title>{data.board.name} — Web App Launcher</title>
 </svelte:head>
 
-<div class="mx-auto max-w-7xl px-4 py-6">
-	<BoardHeader
-		name={data.board.name}
-		description={data.board.description}
-		icon={data.board.icon}
-		boardId={data.board.id}
-		canEdit={data.canEdit}
-	/>
+<div class="p-6">
+	<div class="mx-auto max-w-7xl">
+		<BoardHeader
+			name={data.board.name}
+			description={data.board.description}
+			icon={data.board.icon}
+			boardId={data.board.id}
+			canEdit={data.canEdit}
+		/>
 
-	<Board sections={data.board.sections} />
+		<Board sections={data.board.sections} />
+	</div>
 </div>