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

controllers/api/api.go

@@ -17,6 +17,7 @@ import (
 	"git.golem15.com/golem15/summercms/modules/cooler"
 	"git.golem15.com/golem15/summercms/modules/phrasebook"
 	"git.golem15.com/golem15/summercms/modules/wire"
+	"git.golem15.com/jakub/sm-bm-plugin/classes"
 	"gocloud.dev/blob"
 	"gorm.io/gorm"
 )
@@ -73,6 +74,10 @@ type Handlers struct {
 	// Cache returns the application cache that holds the issued upload
 	// tickets until they are used, or nil while none is available.
 	Cache func() cooler.Cache
+	// MaterialIndex searches the materials index and keeps it current. Nil
+	// means a search (q) answers 503 and the syncs after a write are
+	// skipped.
+	MaterialIndex *classes.MaterialIndexer
 }
 
 func (h *Handlers) now() time.Time {