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/admin/views/WikiEditor.jsx

@@ -15,19 +15,25 @@ export default function WikiEditor({ slug, onClose, onSaved }) {
     excerpt: '',
     category_id: '',
     published: true,
+    tags: '',
   })
   const [categories, setCategories] = useState([])
+  const [pages, setPages] = useState([])
   const [loading, setLoading] = useState(isEdit)
   const [busy, setBusy] = useState(false)
   const [error, setError] = useState('')
 
-  // Categories for the dropdown (both new and edit).
+  // Categories (dropdown) + pages (internal-link picker), for both new and edit.
   useEffect(() => {
     let active = true
     api.admin
       .listWikiCategories()
       .then((cats) => active && setCategories(cats))
       .catch(() => {})
+    api.admin
+      .listWiki()
+      .then((list) => active && setPages(list.map((p) => ({ slug: p.slug, title: p.title }))))
+      .catch(() => {})
     return () => {
       active = false
     }
@@ -48,6 +54,7 @@ export default function WikiEditor({ slug, onClose, onSaved }) {
             excerpt: p.excerpt || '',
             category_id: p.category_id != null ? String(p.category_id) : '',
             published: Boolean(p.published),
+            tags: (p.tags || []).map((t) => t.label).join(', '),
           }),
       )
       .catch(() => active && setError('Could not load this page.'))
@@ -66,6 +73,10 @@ export default function WikiEditor({ slug, onClose, onSaved }) {
       excerpt: form.excerpt.trim(),
       category_id: form.category_id ? Number(form.category_id) : null,
       published: form.published,
+      tags: form.tags
+        .split(',')
+        .map((t) => t.trim())
+        .filter(Boolean),
     }
   }
 
@@ -174,10 +185,24 @@ export default function WikiEditor({ slug, onClose, onSaved }) {
               placeholder="One-line summary shown on the wiki home."
             />
           </label>
+          <label>
+            <span className="field-label">Tags (comma-separated)</span>
+            <input
+              type="text"
+              value={form.tags}
+              onChange={set('tags')}
+              className="input"
+              placeholder="beginner, pvp, towns"
+            />
+          </label>
           <div>
             <span className="field-label">Body (use Heading 2 for table-of-contents sections)</span>
             <Suspense fallback={<span className="spin" />}>
-              <RichTextEditor value={form.body} onChange={(html) => setForm((f) => ({ ...f, body: html }))} />
+              <RichTextEditor
+                value={form.body}
+                onChange={(html) => setForm((f) => ({ ...f, body: html }))}
+                pages={pages.filter((p) => p.slug !== form.slug)}
+              />
             </Suspense>
           </div>
         </div>