Fix missing H1 on list-style pages via SectionHeading template

SectionHeading always rendered its title as <h2>, so every page whose
only heading came from a shared section component (services hub,
promotions, cases, faq, contact, reviews, blog list) had no <h1> at
all. Add a level prop (default h2) and pass headingLevel="h1" from
each page where that section is the page's own top-level heading.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013otXCiTZsxdZ4SJKZ9wUky

public-site/app/blog/page.jsx

@@ -24,7 +24,12 @@ export default async function BlogListPage() {
     <div>
       <Header />
       <section className="max-w-3xl mx-auto px-5 sm:px-8 py-20 min-h-[60vh]">
-        <SectionHeading eyebrow="blog --articles" title="Блог" desc="Заметки об IT-инфраструктуре, кибербезопасности и автоматизации." />
+        <SectionHeading
+          eyebrow="blog --articles"
+          title="Блог"
+          desc="Заметки об IT-инфраструктуре, кибербезопасности и автоматизации."
+          level="h1"
+        />
 
         {posts.length === 0 && <p className="text-sm text-slate-400">Пока нет опубликованных статей - загляните позже.</p>}