refactor: 移除文章系列的前后导航及相关样式

src/routes/posts/[slug]/+page.svelte

@@ -10,15 +10,6 @@
 	let hasToc = $state(false);
 
 	let { data }: { data: PageData } = $props();
-	let currentSeriesIndex = $derived(data.seriesPosts.findIndex((post) => post.id === data.post.id));
-	let previousSeriesPost = $derived(
-		currentSeriesIndex > 0 ? data.seriesPosts[currentSeriesIndex - 1] : null
-	);
-	let nextSeriesPost = $derived(
-		currentSeriesIndex >= 0 && currentSeriesIndex < data.seriesPosts.length - 1
-			? data.seriesPosts[currentSeriesIndex + 1]
-			: null
-	);
 
 	let isSeriesOpen = $state(true);
 	let seriesContentEl: HTMLElement | null = $state(null);
@@ -155,20 +146,6 @@
 									</li>
 								{/each}
 							</ul>
-							{#if previousSeriesPost || nextSeriesPost}
-								<div class="series-prev-next" aria-label="系列文章翻页">
-									{#if previousSeriesPost}
-										<a href={resolve('/posts/[slug]', { slug: previousSeriesPost.slug })}
-											>← {previousSeriesPost.title}</a
-										>
-									{:else}<span></span>{/if}
-									{#if nextSeriesPost}
-										<a href={resolve('/posts/[slug]', { slug: nextSeriesPost.slug })}
-											>{nextSeriesPost.title} →</a
-										>
-									{/if}
-								</div>
-							{/if}
 						</nav>
 					</div>
 				</div>
@@ -314,36 +291,4 @@
 	.series-nav li a:hover {
 		color: var(--accent-color, #419b38);
 	}
-
-	/* 系列前后导航 — BlogFlare 自有功能 */
-	.series-nav .series-prev-next {
-		display: grid;
-		grid-template-columns: 1fr 1fr;
-		gap: 1rem;
-		padding: 0.8rem 1rem;
-		border-top: 1px dashed var(--border-color, rgba(0, 0, 0, 0.12));
-		font-size: 0.9em;
-	}
-
-	.series-nav .series-prev-next a {
-		color: var(--text-color);
-		text-decoration: none;
-	}
-
-	.series-nav .series-prev-next a:hover {
-		color: var(--accent-color, #419b38);
-	}
-
-	.series-nav .series-prev-next a:last-child {
-		text-align: right;
-	}
-
-	@media (max-width: 640px) {
-		.series-nav .series-prev-next {
-			grid-template-columns: 1fr;
-		}
-		.series-nav .series-prev-next a:last-child {
-			text-align: left;
-		}
-	}
 </style>