feat(mvp): phase 5 - board, section & widget system

Add board/section/widget CRUD APIs with permission filtering, board view
page with collapsible sections and app widgets in responsive grid, form-based
board editor, and 9 Svelte components (Board, Section, Widget families).

src/routes/boards/[boardId]/+page.server.ts

@@ -0,0 +1,61 @@
+import { error } from '@sveltejs/kit';
+import type { PageServerLoad } from './$types.js';
+import * as boardService from '$lib/server/services/boardService.js';
+import * as permissionService from '$lib/server/services/permissionService.js';
+import { EntityType, PermissionLevel, UserRole } from '$lib/utils/constants.js';
+import { isBoardGuestAccessible } from '$lib/server/middleware/guestAccess.js';
+
+export const load: PageServerLoad = async ({ params, locals }) => {
+	const { boardId } = params;
+	const user = locals.user;
+
+	// Permission check
+	if (!user) {
+		const isGuest = await isBoardGuestAccessible(boardId);
+		if (!isGuest) {
+			throw error(401, { message: 'Authentication required' });
+		}
+	} else if (user.role !== UserRole.ADMIN) {
+		const result = await permissionService.checkPermission(
+			EntityType.BOARD,
+			boardId,
+			user.id,
+			PermissionLevel.VIEW
+		);
+		if (!result.hasPermission) {
+			const isGuest = await isBoardGuestAccessible(boardId);
+			if (!isGuest) {
+				throw error(403, { message: 'Insufficient permissions' });
+			}
+		}
+	}
+
+	try {
+		// findBoardById includes sections -> widgets -> app -> statuses
+		const board = await boardService.findBoardById(boardId);
+
+		// Determine if user can edit this board
+		let canEdit = false;
+		if (user) {
+			if (user.role === UserRole.ADMIN) {
+				canEdit = true;
+			} else {
+				const editResult = await permissionService.checkPermission(
+					EntityType.BOARD,
+					boardId,
+					user.id,
+					PermissionLevel.EDIT
+				);
+				canEdit = editResult.hasPermission;
+			}
+		}
+
+		return { board, canEdit };
+	} catch (err) {
+		const message = err instanceof Error ? err.message : 'Board not found';
+		if (message.includes('not found')) {
+			throw error(404, { message: 'Board not found' });
+		}
+		throw error(500, { message });
+	}
+};