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>

server/src/router/v1/admin/admin.controller.js

@@ -160,6 +160,15 @@ async function uploadImage(req, res) {
   return res.status(201).json({ image_url: imageUrl })
 }
 
+// Generalized upload used by rich-text editors (wiki, etc.). Same multer config
+// as the screenshot upload; returns a neutral { url }.
+async function uploadFile(req, res) {
+  if (!req.file) return res.status(400).json({ message: 'No file uploaded' })
+  const url = `/uploads/${req.file.filename}`
+  await activity.log({ req, action: 'upload', detail: { url } })
+  return res.status(201).json({ url })
+}
+
 // ── Wiki pages ─────────────────────────────────────────────────────────
 async function listWiki(req, res) {
   try {
@@ -457,6 +466,7 @@ module.exports = {
   publishPost,
   deletePost,
   uploadImage,
+  uploadFile,
   listWiki,
   getWiki,
   createWiki,