Astro 7へ更新し、画像をsrc/へ移行・重複を整理

- astro 6→7 / starlight 0.40→0.42 / sharp更新、markdown-remark導入
- markdownをunified()へ移行、compressHTML:trueで従来の空白を維持
- starlight日本語訳パッチを0.42.5向けに再生成
- 有益な画像をsrc/へ移行しpublic重複を削除、孤立画像を整理
- scripts/optimize-images.mjs を追加（prebuildで自動実行）

1 files changed, 12 insertions, 3 deletions

diff --git a/src/styles/custom.css b/src/styles/custom.css
index 856bfe1..1a62595 100644
--- a/src/styles/custom.css
+++ b/src/styles/custom.css
@@ -859,8 +859,7 @@ main:has(.home-hero) {
   position: relative;
   margin: 3.5rem calc(-50vw + 50%) 3rem calc(-50vw + 50%);
   padding: 6rem 1rem 5rem 8%;
-  background: url("/img/mini_yasutake-yohei_15.jpg") top center/auto 110%
-    no-repeat;
+  overflow: hidden;
   text-align: left;
   color: #fff;
   min-height: 320px;
@@ -875,6 +874,16 @@ main:has(.home-hero) {
   inset: 0;
   background: none;
 }
+/* Hero background image (optimized via astro:assets) */
+.home-hero .hero-bg {
+  position: absolute;
+  inset: 0;
+  width: 100%;
+  height: 100%;
+  object-fit: cover;
+  object-position: top center;
+  z-index: 0;
+}
 .home-hero > * {
   position: relative;
   z-index: 1;
@@ -959,7 +968,7 @@ main:has(.home-hero) {
 }
 .home-sep span {
   font-size: 0.85rem;
-  color: #888;
+  color: #666;
   font-weight: 600;
 }