SNS共有: twitter:card追加、見出しアンカーを常時表示に改善

- twitter:card=summary_large_image を追加し、Xでの共有表示を最適化
- 見出しアンカーを常時表示（opacity: 0.3）に変更
  クリックで「コピーしました！」のフィードバック表示も追加
- OGPはStarlightが自動生成済み（title/description/image/url）

2 files changed, 15 insertions, 5 deletions

diff --git a/astro.config.mjs b/astro.config.mjs
index 6f7f212..b87a554 100644
--- a/astro.config.mjs
+++ b/astro.config.mjs
@@ -186,6 +186,13 @@ export default defineConfig({
           },
         },
         {
+          tag: "meta",
+          attrs: {
+            name: "twitter:card",
+            content: "summary_large_image",
+          },
+        },
+        {
           tag: "script",
           attrs: { type: "application/ld+json" },
           content: JSON.stringify({
@@ -225,7 +232,7 @@ export default defineConfig({
         {
           tag: "script",
           content:
-            "document.addEventListener('DOMContentLoaded', () => { document.querySelectorAll('.sl-markdown-content h2[id], .sl-markdown-content h3[id]').forEach(h => { const a = document.createElement('a'); a.href = '#' + h.id; a.className = 'heading-anchor'; a.innerHTML = '<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"16\" height=\"16\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71\"/><path d=\"M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71\"/></svg>'; a.title = 'この見出しへのリンクをコピー'; a.addEventListener('click', e => { e.preventDefault(); const url = location.origin + location.pathname + '#' + h.id; navigator.clipboard.writeText(url).then(() => { a.classList.add('copied'); setTimeout(() => a.classList.remove('copied'), 1500); }); }); h.prepend(a); }); });",
+            "document.addEventListener('DOMContentLoaded', () => { document.querySelectorAll('.sl-markdown-content h2[id], .sl-markdown-content h3[id]').forEach(h => { const a = document.createElement('a'); a.href = '#' + h.id; a.className = 'heading-anchor'; a.innerHTML = '<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71\"/><path d=\"M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71\"/></svg>'; a.title = 'クリックでこの見出しのURLをコピー'; a.addEventListener('click', e => { e.preventDefault(); const url = location.origin + location.pathname + '#' + h.id; navigator.clipboard.writeText(url).then(() => { a.classList.add('copied'); a.title = 'コピーしました！'; setTimeout(() => { a.classList.remove('copied'); a.title = 'クリックでこの見出しのURLをコピー'; }, 2000); }); }); h.prepend(a); }); });",
         },
         {
           tag: "script",
diff --git a/src/styles/custom.css b/src/styles/custom.css
index f765954..f43e7ff 100644
--- a/src/styles/custom.css
+++ b/src/styles/custom.css
@@ -1051,22 +1051,25 @@ main:has(.home-hero) {
 
 /* ── Heading Anchor Links ── */
 .heading-anchor {
-  opacity: 0;
+  opacity: 0.3;
   margin-left: -1.2em;
   padding-right: 0.3em;
   color: var(--sl-color-gray-3);
   text-decoration: none;
-  transition: opacity 0.2s;
+  transition:
+    opacity 0.2s,
+    color 0.2s;
   float: left;
 }
 h2:hover .heading-anchor,
-h3:hover .heading-anchor,
-.heading-anchor.copied {
+h3:hover .heading-anchor {
   opacity: 1;
 }
 .heading-anchor:hover {
   color: var(--sl-color-accent);
+  opacity: 1;
 }
 .heading-anchor.copied {
+  opacity: 1;
   color: var(--sl-color-green-high, #16a34a);
 }