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/components/sections/Cases.jsx

@@ -3,13 +3,13 @@ import Reveal from '../Reveal.jsx';
 import SectionHeading from '../SectionHeading.jsx';
 import StatusDot from '../StatusDot.jsx';
 
-export default function Cases({ cases, limit, moreHref, showDisclaimer = false }) {
+export default function Cases({ cases, limit, moreHref, showDisclaimer = false, headingLevel = 'h2' }) {
   if (cases.length === 0) return null;
   const list = limit ? cases.slice(0, limit) : cases;
 
   return (
     <section id="cases" className="max-w-6xl mx-auto px-5 sm:px-8 py-20">
-      <SectionHeading eyebrow="cases --log" title="Кейсы и портфолио" />
+      <SectionHeading eyebrow="cases --log" title="Кейсы и портфолио" level={headingLevel} />
       <div className="grid sm:grid-cols-2 lg:grid-cols-3 gap-5">
         {list.map((c, i) => (
           <Reveal key={c.id} delay={i * 60}>