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/lib/components/board/Board.svelte

@@ -0,0 +1,45 @@
+<script lang="ts">
+	import Section from '$lib/components/section/Section.svelte';
+
+	interface SectionData {
+		id: string;
+		title: string;
+		icon: string | null;
+		order: number;
+		isExpandedByDefault: boolean;
+		widgets: Array<{
+			id: string;
+			type: string;
+			order: number;
+			config: string;
+			appId: string | null;
+			app: {
+				id: string;
+				name: string;
+				url: string;
+				icon: string | null;
+				iconType: string;
+				description: string | null;
+				statuses: Array<{ status: string; responseTime: number | null }>;
+			} | null;
+		}>;
+	}
+
+	interface Props {
+		sections: SectionData[];
+	}
+
+	let { sections }: Props = $props();
+</script>
+
+<div class="space-y-6">
+	{#if sections.length === 0}
+		<div class="rounded-lg border border-gray-700 bg-gray-800/50 p-12 text-center">
+			<p class="text-gray-400">This board has no sections yet.</p>
+		</div>
+	{:else}
+		{#each sections as section (section.id)}
+			<Section {section} />
+		{/each}
+	{/if}
+</div>