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/styles/theme.css

@@ -447,6 +447,86 @@ button[disabled] {
   border-bottom: 1px dotted #d98b84;
 }
 
+/* ===== Wiki revision history ===== */
+.wiki-history {
+  display: grid;
+  grid-template-columns: 240px 1fr;
+  gap: 18px;
+  align-items: start;
+}
+@media (max-width: 640px) {
+  .wiki-history {
+    grid-template-columns: 1fr;
+  }
+}
+.wiki-history-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+  max-height: 360px;
+  overflow-y: auto;
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+.wiki-rev {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  width: 100%;
+  padding: 8px 10px;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  background: var(--panel-flat);
+  color: var(--text);
+  text-align: left;
+  cursor: pointer;
+}
+.wiki-rev:hover {
+  border-color: var(--accent);
+}
+.wiki-rev.is-active {
+  border-color: var(--accent);
+  background: var(--blue);
+}
+.wiki-rev-note {
+  font-family: var(--sans);
+  font-size: 0.86rem;
+  color: var(--head);
+}
+.wiki-rev-latest {
+  color: var(--accent);
+  font-size: 0.74rem;
+}
+.wiki-rev-meta {
+  font-family: var(--sans);
+  font-size: 0.72rem;
+  color: var(--dim);
+}
+.wiki-diff {
+  white-space: pre-wrap;
+  word-break: break-word;
+  font-family: var(--sans);
+  font-size: 0.92rem;
+  line-height: 1.6;
+  color: var(--text);
+  max-height: 360px;
+  overflow-y: auto;
+  padding: 12px 14px;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  background: var(--bg);
+}
+.diff-add {
+  background: rgba(95, 185, 138, 0.22);
+  color: #b9e6cd;
+}
+.diff-del {
+  background: rgba(176, 102, 95, 0.24);
+  color: #e3b0aa;
+  text-decoration: line-through;
+}
+
 /* ===== Admin tables ===== */
 .adm-table {
   width: 100%;