Wiki Phase 4: full-text search + revision history

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

Schema (additive): wiki_revisions table (per-save content snapshots).
The FULLTEXT index on wiki_pages(title, body) shipped in Phase 1.

Search:
- MATCH ... AGAINST natural-language search over title + body, ordered by
  relevance
- public: GET /public/wiki?q= (published only); admin: GET /admin/wiki?q=
  (all statuses)
- public wiki index gains a search box; admin list gains a search field

Revision history:
- every create/update snapshots the page into wiki_revisions
- admin endpoints: list revisions, get one, and restore (restore overwrites
  the page, rebuilds links, and appends a new revision — history stays
  append-only); logged as wiki.revision.restore
- editor gains a History modal: revision list + word-level diff (jsdiff) of a
  chosen revision against the current page, with one-click restore

Verified end-to-end: search matches body and title; two edits produce three
revisions; diff renders added/removed words; restore reverts and records a new
revision. No console errors.

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

client/src/api/client.js

@@ -53,6 +53,7 @@ export const api = {
     const qs = new URLSearchParams()
     if (opts.category) qs.set('category', opts.category)
     if (opts.tag) qs.set('tag', opts.tag)
+    if (opts.q) qs.set('q', opts.q)
     const s = qs.toString()
     return req(`/public/wiki${s ? `?${s}` : ''}`)
   },
@@ -90,6 +91,10 @@ export const api = {
     publishWiki: (slug, published) =>
       req(`/admin/wiki/${slug}/publish`, { method: 'PATCH', body: { published } }),
     deleteWiki: (slug) => req(`/admin/wiki/${slug}`, { method: 'DELETE' }),
+    listWikiRevisions: (slug) => req(`/admin/wiki/${slug}/revisions`),
+    getWikiRevision: (slug, id) => req(`/admin/wiki/${slug}/revisions/${id}`),
+    restoreWikiRevision: (slug, id) =>
+      req(`/admin/wiki/${slug}/revisions/${id}/restore`, { method: 'POST' }),
     listWikiTags: () => req('/admin/wiki/tags'),
     listWikiCategories: () => req('/admin/wiki/categories'),
     createWikiCategory: (data) => req('/admin/wiki/categories', { method: 'POST', body: data }),