feat: search materials through beachcomber

- Material is a beachcomber Searchable (index jz_bm_materials) in the
  hand-written models/material_search.go; jz.bm requires summercms v0.6.4
- classes.MaterialIndexer asks Typesense for up to 250 candidates with
  body highlights; the app-wide Gate is on only for jz.bm-marked contexts
- GET /_bm/api/v1/materials takes q: candidates are re-gated, counted and
  paged in SQL in rank order, each row with at most one plain snippet
- search failure answers 503 Search is unavailable.; without q the list
  is unchanged

search.go

@@ -0,0 +1,23 @@
+package bm
+
+import (
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/beachcomber"
+	_ "git.golem15.com/golem15/summercms/modules/beachcomber/typesense"
+	"git.golem15.com/jakub/sm-bm-plugin/classes"
+)
+
+// wireSearch builds the app's beachcomber service (search.driver; the
+// typesense engine registers itself through the blank import), installs the
+// jz.bm-only Gate and the material indexer. The Gate is app-wide, so it is
+// on only for contexts jz.bm marks: golem15.chatchannels' message syncs stay
+// off and chat messages never reach the index.
+func (p *Plugin) wireSearch(app *backpack.App) error {
+	svc, err := beachcomber.From(app)
+	if err != nil {
+		return err
+	}
+	svc.SetGate(classes.MaterialSearchGate())
+	p.materialIndex = classes.NewMaterialIndexer(app)
+	return nil
+}