feat: add about, contact with map, legal pages and 404

- About page with identity cards and equipment lists (about.json)
- Contact page: station info, obfuscated e-mail, lazy Leaflet/OSM map
  with antenna tower marker and dark-mode tiles
- Privacy, license and disclaimer pages from a legal collection
- QRT-themed 404 page
- LICENSE (MIT) and LICENSE-CONTENT (CC BY-SA 4.0 legal code)
- Shared PageHeader and CodeCopy components

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/components/blog/BlogListing.astro

@@ -4,8 +4,7 @@ import BaseLayout from '../../layouts/BaseLayout.astro';
 import { blog, fmt } from '../../lib/data';
 import type { Post } from '../../lib/posts';
 import Container from '../Container.astro';
-import GridLines from '../GridLines.astro';
-import SectionHeading from '../SectionHeading.astro';
+import PageHeader from '../PageHeader.astro';
 import Pager from './Pager.astro';
 import PostCard from './PostCard.astro';
 import Sidebar from './Sidebar.astro';
@@ -43,13 +42,7 @@ const seoTitle = current > 1 ? fmt(blog.list.pageTitle, { title, n: current }) :
 ---
 
 <BaseLayout title={seoTitle} description={description} jsonLd={jsonLd}>
-  <section class="surface-alt relative overflow-hidden">
-    <GridLines />
-    <Container class="relative py-14 md:py-20">
-      <SectionHeading level={1} eyebrow={eyebrow} title={title} />
-      <p class="mt-4 max-w-2xl text-lg">{description}</p>
-    </Container>
-  </section>
+  <PageHeader eyebrow={eyebrow} title={title} lead={description} />
 
   <Container class="grid gap-12 py-14 lg:grid-cols-[minmax(0,1fr)_20rem]">
     <div>