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/+layout.server.ts

@@ -1,7 +1,40 @@
 import type { LayoutServerLoad } from './$types.js';
+import { prisma } from '$lib/server/prisma.js';
 
 export const load: LayoutServerLoad = async ({ locals }) => {
+	// Fetch sidebar boards for the layout
+	let boards: Array<{ id: string; name: string; icon: string | null }> = [];
+
+	try {
+		if (locals.user) {
+			// Authenticated user: fetch boards they can access
+			if (locals.user.role === 'admin') {
+				boards = await prisma.board.findMany({
+					select: { id: true, name: true, icon: true },
+					orderBy: [{ isDefault: 'desc' }, { name: 'asc' }]
+				});
+			} else {
+				// Regular users: fetch all boards (permission filtering done at page level)
+				boards = await prisma.board.findMany({
+					select: { id: true, name: true, icon: true },
+					orderBy: [{ isDefault: 'desc' }, { name: 'asc' }]
+				});
+			}
+		} else {
+			// Guest: only guest-accessible boards
+			boards = await prisma.board.findMany({
+				where: { isGuestAccessible: true },
+				select: { id: true, name: true, icon: true },
+				orderBy: [{ isDefault: 'desc' }, { name: 'asc' }]
+			});
+		}
+	} catch {
+		// Fail gracefully — sidebar will just be empty
+		boards = [];
+	}
+
 	return {
-		user: locals.user
+		user: locals.user,
+		sidebarBoards: boards
 	};
 };