feat: keep the materials index in sync and add bm:materials-reindex

- the materials admin syncs after create and update and removes after
  delete, once the save transaction commits (UseMaterialIndex, set at Boot)
- POST and PUT /api/v1/bm/materials sync after the transaction, DELETE
  removes the document (its statement has no primary key, so no callback)
- bm:materials-reindex [--fresh] [--if-configured] ensures the index and
  syncs every material; it refuses without an engine and runs nightly
  at 04:15 with --if-configured
- TestMaterialSearchAgainstDatabase (Postgres) is written for the final
  verification phase

internal/searchtest/typesense.go

@@ -130,6 +130,13 @@ func (s *Stub) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// SetHits replaces the answer of every later search.
+func (s *Stub) SetHits(hits ...Hit) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.Hits = hits
+}
+
 // Requests returns the requests received so far.
 func (s *Stub) Requests() []Request {
 	s.mu.Lock()