Restructure navigation around What's up / Opine and the reader's utilities

- Stories gain a required type (report | essay); all 28 classified per
  the boundary rule now stated in EDITORIAL.md
- Nav: What's up · Opine · Podcast · Book · Guides · Forum, each gated
  on real content (Forum waits on a forumUrl); logo is Home
- /whats-up (reports, newest first) and /opine (essays, editorial order)
  share a StoryArchive component with subject filters
- Static /tags/<tag> pages for subjects carried by 2+ stories; tags stay
  overlapping, never exclusive departments
- /corrections: generated from revision history (commits beginning
  'Correction:'), so the page cannot under-report
- About, RSS, Corrections, Weekly briefing move to the footer

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/components/StoryArchive.astro

@@ -0,0 +1,127 @@
+---
+import type { CollectionEntry } from 'astro:content';
+import StoryCard from './StoryCard.astro';
+
+interface Props {
+  title: string;
+  count: string;
+  note?: string;
+  noteHref?: string;
+  entries: CollectionEntry<'stories'>[];
+  emptyMessage: string;
+  activeTag?: string;
+}
+
+const { title, count, note, noteHref, entries, emptyMessage, activeTag } = Astro.props;
+
+const tagCounts = new Map<string, number>();
+for (const entry of entries) {
+  for (const tag of entry.data.tags) {
+    tagCounts.set(tag, (tagCounts.get(tag) ?? 0) + 1);
+  }
+}
+// Only subjects carried by 2+ of the listed stories get a filter link
+// (which also guarantees the target tag page exists).
+const tags = [...tagCounts.entries()]
+  .filter(([, count]) => count >= 2)
+  .sort((a, b) => b[1] - a[1] || a[0].localeCompare(b[0]));
+---
+
+<section class="shell archive-head">
+  <h1>{title}</h1>
+  <p>{count}{note && noteHref && <a href={noteHref}>{note}</a>}</p>
+</section>
+{tags.length > 1 && (
+  <nav class="shell tag-row" aria-label="Browse by subject">
+    {tags.map(([tag, n]) => (
+      <a href={`/tags/${tag}`} class:list={{ active: tag === activeTag }}>{tag}<span>{n}</span></a>
+    ))}
+  </nav>
+)}
+<section class="shell archive-list">
+  {entries.length > 0 ? entries.map((entry, index) => <StoryCard entry={entry} index={index} />) : <p class="empty-state">{emptyMessage}</p>}
+</section>
+
+<style>
+  .archive-head {
+    display: flex;
+    align-items: baseline;
+    justify-content: space-between;
+    gap: 1.5rem;
+    padding: clamp(1.6rem, 4vw, 3.25rem) 0 1rem;
+    border-bottom: 1px solid var(--ink);
+  }
+
+  .archive-head h1 {
+    margin: 0;
+    font-family: 'Newsreader Variable', Georgia, serif;
+    font-size: clamp(2.4rem, 5vw, 4.5rem);
+    font-weight: 560;
+    letter-spacing: -0.045em;
+    line-height: 0.9;
+  }
+
+  .archive-head p {
+    margin: 0;
+    color: var(--muted);
+    font-family: 'IBM Plex Mono', monospace;
+    font-size: 0.65rem;
+    text-transform: uppercase;
+  }
+
+  .archive-head a {
+    margin-left: 1rem;
+    color: var(--blue);
+  }
+
+  .tag-row {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 0.4rem 0.9rem;
+    padding: 0.85rem 0;
+  }
+
+  .tag-row a {
+    color: var(--muted);
+    font-family: 'IBM Plex Mono', monospace;
+    font-size: 0.66rem;
+    letter-spacing: 0.04em;
+    text-decoration: none;
+    text-transform: uppercase;
+  }
+
+  .tag-row a:hover,
+  .tag-row a.active {
+    color: var(--ink);
+    text-decoration: underline;
+    text-underline-offset: 0.25em;
+  }
+
+  .tag-row span {
+    margin-left: 0.3rem;
+    color: var(--rule);
+  }
+
+  .tag-row a:hover span,
+  .tag-row a.active span {
+    color: var(--amend);
+  }
+
+  .archive-list {
+    display: grid;
+    grid-template-columns: repeat(3, minmax(0, 1fr));
+    gap: 1px;
+    margin-top: 1px;
+    border: 1px solid var(--rule);
+    background: var(--rule);
+  }
+
+  @media (max-width: 900px) {
+    .archive-list { grid-template-columns: repeat(2, minmax(0, 1fr)); }
+  }
+
+  @media (max-width: 620px) {
+    .archive-head { align-items: flex-start; flex-direction: column; gap: 0.65rem; }
+    .archive-list { grid-template-columns: 1fr; }
+  }
+</style>