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/components/RichTextEditor.jsx

@@ -21,9 +21,15 @@ function Btn({ onClick, active, disabled, title, children }) {
   )
 }
 
-export default function RichTextEditor({ value, onChange }) {
+function escapeHtml(s) {
+  return String(s).replace(/[&<>"]/g, (c) => ({ '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;' })[c])
+}
+
+export default function RichTextEditor({ value, onChange, pages = [] }) {
   const fileRef = useRef(null)
   const [uploading, setUploading] = useState(false)
+  const [linkMenu, setLinkMenu] = useState(false)
+  const [linkFilter, setLinkFilter] = useState('')
 
   const editor = useEditor({
     extensions: [
@@ -55,6 +61,17 @@ export default function RichTextEditor({ value, onChange }) {
     editor.chain().focus().extendMarkRange('link').setLink({ href: url }).run()
   }
 
+  function insertInternalLink(page) {
+    const { from, to } = editor.state.selection
+    if (from === to) {
+      editor.chain().focus().insertContent(`<a href="/wiki/${page.slug}">${escapeHtml(page.title)}</a> `).run()
+    } else {
+      editor.chain().focus().extendMarkRange('link').setLink({ href: `/wiki/${page.slug}` }).run()
+    }
+    setLinkMenu(false)
+    setLinkFilter('')
+  }
+
   async function onPickImage(e) {
     const file = e.target.files?.[0]
     e.target.value = '' // allow re-selecting the same file
@@ -109,6 +126,9 @@ export default function RichTextEditor({ value, onChange }) {
         <Btn title="Link" active={editor.isActive('link')} onClick={setLink}>
           🔗
         </Btn>
+        <Btn title="Link to another wiki page" disabled={pages.length === 0} onClick={() => setLinkMenu((v) => !v)}>
+          📄
+        </Btn>
         <Btn title="Insert image" disabled={uploading} onClick={() => fileRef.current?.click()}>
           {uploading ? '…' : '🖼'}
         </Btn>
@@ -121,6 +141,32 @@ export default function RichTextEditor({ value, onChange }) {
         </Btn>
       </div>
 
+      {linkMenu && (
+        <div className="rte-linkmenu">
+          <input
+            autoFocus
+            className="input"
+            placeholder="Filter pages…"
+            value={linkFilter}
+            onChange={(e) => setLinkFilter(e.target.value)}
+          />
+          <div className="rte-linkmenu-list">
+            {pages
+              .filter((p) => {
+                const q = linkFilter.trim().toLowerCase()
+                return !q || p.title.toLowerCase().includes(q) || p.slug.includes(q)
+              })
+              .slice(0, 30)
+              .map((p) => (
+                <button key={p.slug} type="button" className="rte-linkmenu-item" onClick={() => insertInternalLink(p)}>
+                  <span>{p.title}</span>
+                  <span className="rte-linkmenu-slug">/{p.slug}</span>
+                </button>
+              ))}
+          </div>
+        </div>
+      )}
+
       <EditorContent editor={editor} className="rte-content prose" />
       <input ref={fileRef} type="file" accept="image/*" onChange={onPickImage} hidden />
     </div>