feat(web): /search two-pane screen (debounced query, visibility filter, load more) + nav

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/i18n/en.json

@@ -18,6 +18,16 @@
     "title": "Authorities", "person": "Person", "organisation": "Organisation", "place": "Place",
     "new": "New", "create": "Create", "empty": "No authorities yet", "loadError": "Could not load"
   },
+  "search": {
+    "placeholder": "Search the collection…",
+    "all": "All",
+    "prompt": "Type to search",
+    "empty": "No results",
+    "loadError": "Search is unavailable",
+    "loadMore": "Load more",
+    "resultCount": "{{count}} results",
+    "selectPrompt": "Select a result to see the full record"
+  },
   "publish": {
     "heading": "Visibility",
     "advanceInternal": "Advance to internal",