feat: 文章正文图片支持灯箱；删除未使用的 GitHub Card 插件

灯箱
- 相册页原本已有一套无依赖灯箱（事件委托 + ClientRouter 友好），
  但它写在 gallery/[album].astro 里，只有相册页能用。
  现抽成 src/components/ImageLightbox.astro，挂到 BaseLayout，全站可用。
- 新增 src/plugins/rehype-image-lightbox.mjs：给正文里的 <img> 注入
  data-lightbox-src。跳过链接内的图片（点击应跳转）和显式标记
  data-lightbox-ignore 的图片。
- 顺带让灯箱大图继承原图的 alt 文本（原先固定为空）。
- 正文图片加 cursor: zoom-in 提示。

清理
- 删除 src/plugins/rehype-component-github-card.mjs（165 行）及其在
  rehypeComponents 里的 github 映射：内容里从未使用过 ::github 指令。

验证：构建 41 页通过；文章页正文图片 4/4 带上 data-lightbox-src，
相册页 5 个触发元素不受影响；灯箱脚本按页内联（2.8KB 压缩后）；
正文渲染文本与线上基线一致，无回归。

src/pages/gallery/[album].astro

@@ -122,115 +122,3 @@ const description = album.description ?? "相册"
     break-inside: avoid;
   }
 </style>
-
-<script>
-  /**
-   * 无依赖灯箱。
-   * 用事件委托 + 每次打开时重新收集当前页的照片，因此 ClientRouter 切页后依然有效。
-   */
-  const LB_ID = "vv-lightbox"
-
-  const ensureOverlay = (): HTMLElement => {
-    let overlay = document.getElementById(LB_ID)
-    if (overlay) return overlay
-
-    overlay = document.createElement("div")
-    overlay.id = LB_ID
-    overlay.setAttribute("role", "dialog")
-    overlay.setAttribute("aria-modal", "true")
-    overlay.className =
-      "fixed inset-0 z-[100] hidden items-center justify-center bg-black/90 backdrop-blur-sm"
-    overlay.innerHTML = `
-      <button type="button" data-lb-close aria-label="关闭"
-        class="absolute right-4 top-4 z-10 flex h-10 w-10 items-center justify-center rounded-full bg-white/10 text-2xl leading-none text-white/90 transition-colors hover:bg-white/20">×</button>
-      <button type="button" data-lb-prev aria-label="上一张"
-        class="absolute left-3 z-10 flex h-11 w-11 items-center justify-center rounded-full bg-white/10 text-2xl leading-none text-white/90 transition-colors hover:bg-white/20 sm:left-6">‹</button>
-      <button type="button" data-lb-next aria-label="下一张"
-        class="absolute right-3 z-10 flex h-11 w-11 items-center justify-center rounded-full bg-white/10 text-2xl leading-none text-white/90 transition-colors hover:bg-white/20 sm:right-6">›</button>
-      <img data-lb-img src="" alt="" class="max-h-[88vh] max-w-[92vw] object-contain" />
-      <div data-lb-count
-        class="absolute bottom-5 left-1/2 -translate-x-1/2 rounded-full bg-white/10 px-3 py-1 font-mono text-xs text-white/80"></div>
-    `
-    document.body.appendChild(overlay)
-    return overlay
-  }
-
-  let sources: string[] = []
-  let current = 0
-
-  const render = (overlay: HTMLElement) => {
-    const img = overlay.querySelector<HTMLImageElement>("[data-lb-img]")
-    const counter = overlay.querySelector<HTMLElement>("[data-lb-count]")
-    if (img) img.src = sources[current] ?? ""
-    if (counter) counter.textContent = `${current + 1} / ${sources.length}`
-    const single = sources.length < 2
-    for (const sel of ["[data-lb-prev]", "[data-lb-next]"]) {
-      const el = overlay.querySelector<HTMLElement>(sel)
-      if (el) el.style.display = single ? "none" : ""
-    }
-  }
-
-  const openAt = (index: number) => {
-    const overlay = ensureOverlay()
-    current = index
-    render(overlay)
-    overlay.classList.remove("hidden")
-    overlay.classList.add("flex")
-    document.body.style.overflow = "hidden"
-  }
-
-  const close = () => {
-    const overlay = document.getElementById(LB_ID)
-    if (!overlay) return
-    overlay.classList.add("hidden")
-    overlay.classList.remove("flex")
-    document.body.style.overflow = ""
-  }
-
-  const step = (delta: number) => {
-    if (sources.length < 2) return
-    current = (current + delta + sources.length) % sources.length
-    const overlay = document.getElementById(LB_ID)
-    if (overlay) render(overlay)
-  }
-
-  if (!(window as unknown as { __vvLightboxBound?: boolean }).__vvLightboxBound) {
-    ;(window as unknown as { __vvLightboxBound?: boolean }).__vvLightboxBound = true
-
-    document.addEventListener("click", (event) => {
-      const target = event.target as Element | null
-
-      const trigger = target?.closest<HTMLElement>("[data-lightbox-src]")
-      if (trigger) {
-        // 每次打开都重新收集当前页的照片
-        const all = Array.from(document.querySelectorAll<HTMLElement>("[data-lightbox-src]"))
-        sources = all.map((el) => el.dataset.lightboxSrc ?? "")
-        openAt(Number(trigger.dataset.lightboxIndex ?? all.indexOf(trigger)))
-        return
-      }
-
-      if (target?.closest("[data-lb-close]")) return close()
-      if (target?.closest("[data-lb-prev]")) return step(-1)
-      if (target?.closest("[data-lb-next]")) return step(1)
-
-      // 点背景关闭（点图片本身不关）
-      const overlay = document.getElementById(LB_ID)
-      if (overlay && target === overlay) close()
-    })
-
-    document.addEventListener("keydown", (event) => {
-      const overlay = document.getElementById(LB_ID)
-      if (!overlay || overlay.classList.contains("hidden")) return
-      if (event.key === "Escape") close()
-      if (event.key === "ArrowLeft") step(-1)
-      if (event.key === "ArrowRight") step(1)
-    })
-
-    // 切页时收拾干净，避免残留遮罩锁住滚动
-    document.addEventListener("astro:page-load", () => {
-      const overlay = document.getElementById(LB_ID)
-      if (overlay) overlay.remove()
-      document.body.style.overflow = ""
-    })
-  }
-</script>