Wiki Phase 3: internal links, backlinks, and tags

Connectivity phase of the wiki upgrade (see WIKI_UPGRADE.md).

Schema (additive new tables): wiki_tags, wiki_page_tags, wiki_links.

Internal links & backlinks:
- new wiki.links.js parses a saved body for /wiki/<slug> (and data-wiki-slug)
  targets; wiki_links is rebuilt on every save
- article shows a "Linked from" section (published backlinks) and renders
  links to non-existent pages as red links (server returns missing_links)
- editor gains an internal-link picker listing existing pages

Tags:
- pages accept a tags[] array; tags upsert on save, page tag-set is replaced,
  and orphaned tags are auto-pruned (on save and delete)
- public/admin list filter by ?tag=; /wiki/tags lists tags with published counts
- article shows tag chips; the index has a flat tag-filtered view; editor has a
  comma-separated tags field

Verified end-to-end: A->B backlink appears, red link detected, link index
rebuilds on edit, tag filtering + chips + pruning all work.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/src/routes/wiki/Wiki.jsx

@@ -38,17 +38,22 @@ function PageCard({ page }) {
 export default function Wiki() {
   const [searchParams] = useSearchParams()
   const activeCategory = searchParams.get('category')
-  const { loading, error, data } = useAsync(() =>
-    Promise.all([api.wikiCategories(), api.wiki()]).then(([categories, pages]) => ({
-      categories,
-      pages,
-    })),
+  const activeTag = searchParams.get('tag')
+  // Tag view fetches a tag-filtered page list; otherwise all pages (grouped here).
+  const { loading, error, data } = useAsync(
+    () =>
+      Promise.all([api.wikiCategories(), api.wiki(activeTag ? { tag: activeTag } : {})]).then(
+        ([categories, pages]) => ({ categories, pages }),
+      ),
+    [activeTag],
   )
+
   const allSections = data ? groupByCategory(data.categories, data.pages) : []
   const sections = activeCategory
     ? allSections.filter((s) => s.slug === activeCategory)
     : allSections
   const hasPages = data && data.pages.length > 0
+  const filtered = Boolean(activeCategory || activeTag)
 
   return (
     <PublicLayout section="wiki">
@@ -61,39 +66,54 @@ export default function Wiki() {
         />
         {loading && <Loading />}
         {error && <ErrorState message="Could not load the wiki right now." />}
-        {!loading && !error && !hasPages && <EmptyState>No wiki pages yet.</EmptyState>}
+        {!loading && !error && !hasPages && !filtered && <EmptyState>No wiki pages yet.</EmptyState>}
 
-        {!loading && !error && activeCategory && (
+        {!loading && !error && filtered && (
           <p className="sans" style={{ margin: '0 0 8px', fontSize: '0.85rem' }}>
             <Link to="/wiki" style={{ color: 'var(--accent)', textDecoration: 'none' }}>
               ← All sections
             </Link>
+            {activeTag && <span className="muted"> · Tagged #{activeTag}</span>}
           </p>
         )}
-        {!loading && !error && hasPages && activeCategory && sections.length === 0 && (
-          <EmptyState>No pages in this section yet.</EmptyState>
-        )}
 
-        {sections.map((section) => (
-          <section key={section.id} style={{ marginTop: 36 }}>
-            <h2
-              className="display"
-              style={{ margin: '0 0 4px', fontSize: '1.5rem', color: 'var(--accent)' }}
-            >
-              {section.title}
-            </h2>
-            {section.description && (
-              <p className="muted" style={{ margin: '0 0 16px', fontSize: '0.95rem' }}>
-                {section.description}
-              </p>
-            )}
-            <div className="grid-4" style={{ marginTop: section.description ? 0 : 12 }}>
-              {section.pages.map((p) => (
+        {/* Tag view: a flat list of matching pages (tags cross categories). */}
+        {!loading && !error && activeTag &&
+          (data.pages.length === 0 ? (
+            <EmptyState>No pages with this tag.</EmptyState>
+          ) : (
+            <div className="grid-4" style={{ marginTop: 12 }}>
+              {data.pages.map((p) => (
                 <PageCard key={p.slug} page={p} />
               ))}
             </div>
-          </section>
-        ))}
+          ))}
+
+        {/* Category / full view: grouped sections. */}
+        {!loading && !error && !activeTag && hasPages && activeCategory && sections.length === 0 && (
+          <EmptyState>No pages in this section yet.</EmptyState>
+        )}
+        {!activeTag &&
+          sections.map((section) => (
+            <section key={section.id} style={{ marginTop: 36 }}>
+              <h2
+                className="display"
+                style={{ margin: '0 0 4px', fontSize: '1.5rem', color: 'var(--accent)' }}
+              >
+                {section.title}
+              </h2>
+              {section.description && (
+                <p className="muted" style={{ margin: '0 0 16px', fontSize: '0.95rem' }}>
+                  {section.description}
+                </p>
+              )}
+              <div className="grid-4" style={{ marginTop: section.description ? 0 : 12 }}>
+                {section.pages.map((p) => (
+                  <PageCard key={p.slug} page={p} />
+                ))}
+              </div>
+            </section>
+          ))}
       </div>
     </PublicLayout>
   )