Use section id instead of array index for element id and sidebar link href

Co-authored-by: na-trium-144 <100704180+na-trium-144@users.noreply.github.com>

Author: Copilot

app/[docs_id]/pageContent.tsx

@@ -87,10 +87,10 @@ export function PageContent(props: PageContentProps) {
       }}
     >
       {dynamicMdContent.map((section, index) => (
-        <Fragment key={index}>
+        <Fragment key={section.id}>
           <div
             className="min-w-1/2 max-w-200 text-justify"
-            id={`${index}`} // 目次からaタグで飛ぶために必要
+            id={section.id} // 目次からaタグで飛ぶために必要
             ref={(el) => {
               sectionRefs.current[index] = el;
             }}

app/sidebar.tsx

@@ -195,11 +195,11 @@ export function Sidebar({ pagesList }: { pagesList: LanguageEntry[] }) {
                               idx + 1 === currentSectionIndex;
                             return (
                               <li
-                                key={idx}
+                                key={section.id}
                                 style={{ marginLeft: section.level - 2 + "em" }}
                               >
                                 <Link
-                                  href={`#${idx + 1}`}
+                                  href={`#${section.id}`}
                                   className={
                                     isCurrentSection ? "font-bold" : ""
                                   }