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/routes/admin/views/WikiAdmin.jsx

@@ -9,7 +9,11 @@ import WikiCategories from './WikiCategories.jsx'
 export default function WikiAdmin() {
   const [tick, setTick] = useState(0)
   const reload = useCallback(() => setTick((t) => t + 1), [])
-  const { loading, error, data } = useAsync(() => api.admin.listWiki(), [tick])
+  const [q, setQ] = useState('')
+  const { loading, error, data } = useAsync(
+    () => api.admin.listWiki(q.trim() ? `?q=${encodeURIComponent(q.trim())}` : ''),
+    [tick, q],
+  )
   const [editing, setEditing] = useState(null) // null | 'new' | slug
   const [managingCats, setManagingCats] = useState(false)
   const pages = data || []
@@ -21,6 +25,14 @@ export default function WikiAdmin() {
           {pages.length} page{pages.length === 1 ? '' : 's'} · edit content and structure
         </p>
         <div style={{ display: 'flex', gap: 10 }}>
+          <input
+            type="search"
+            value={q}
+            onChange={(e) => setQ(e.target.value)}
+            className="input"
+            placeholder="Search pages…"
+            style={{ width: 200 }}
+          />
           <button onClick={() => setManagingCats(true)} className="pill">
             Manage sections
           </button>