Wiki Phase 2: TipTap rich-text editor + inline image uploads

Replaces the raw-HTML textarea in the wiki editor with a TipTap (ProseMirror)
WYSIWYG editor.

- new RichTextEditor component: bold/italic/strike, H2/H3, bullet+ordered
  lists, blockquote, code block, divider, link, inline image, undo/redo
- generalized POST /admin/uploads (reuses the screenshot multer config) →
  { url }; the editor uploads inline images through it
- editor output still passes through the Phase 1 server-side sanitizer on
  save and DOMPurify on render
- lazy-loaded as its own chunk so the public bundle doesn't ship TipTap
  (public ~82kB gzip; editor chunk ~106kB gzip loaded only in admin)
- RTE styling added to theme.css (toolbar, active states, prose content)

Verified: uploads serve as images; H2/H3 + lists + link + inline image
round-trip through the WYSIWYG and render sanitized on the public page.

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

client/src/routes/admin/views/WikiEditor.jsx

@@ -1,7 +1,11 @@
-import { useEffect, useState } from 'react'
+import { lazy, Suspense, useEffect, useState } from 'react'
 import Modal from '../../../components/Modal.jsx'
 import { api } from '../../../api/client.js'
 
+// Admin-only and heavy (TipTap) — load as its own chunk so the public bundle
+// never pays for it.
+const RichTextEditor = lazy(() => import('../../../components/RichTextEditor.jsx'))
+
 export default function WikiEditor({ slug, onClose, onSaved }) {
   const isEdit = Boolean(slug)
   const [form, setForm] = useState({
@@ -170,10 +174,12 @@ export default function WikiEditor({ slug, onClose, onSaved }) {
               placeholder="One-line summary shown on the wiki home."
             />
           </label>
-          <label>
-            <span className="field-label">Body (HTML — use &lt;h2&gt; for the table of contents)</span>
-            <textarea value={form.body} onChange={set('body')} className="textarea" style={{ minHeight: 260 }} />
-          </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 }))} />
+            </Suspense>
+          </div>
         </div>
       )}
     </Modal>