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

plugin.go

@@ -59,6 +59,9 @@ type Plugin struct {
 	// chatMember is the chat-group check of the realtime access guard; nil
 	// means classes.IsChatMember. Tests inject their own.
 	chatMember classes.MemberFunc
+	// materialIndex searches the materials index and keeps it current. Nil
+	// when Boot did not run: then search answers 503 and syncs are skipped.
+	materialIndex *classes.MaterialIndexer
 }
 
 func (p *Plugin) ID() string { return "jz.bm" }
@@ -74,7 +77,8 @@ func (p *Plugin) Register(app *backpack.App) error {
 
 // Boot keeps the application, so route handlers and commands can reach its
 // services, such as the database, when they run, and wires the realtime
-// service and, when golem15.chat is active, the BM chat context. The
+// service, the materials search and, when golem15.chat is active, the BM
+// chat context. The
 // management API uses the shared user.api_token middleware owned by
 // golem15.user.
 func (p *Plugin) Boot(app *backpack.App) error {
@@ -83,6 +87,9 @@ func (p *Plugin) Boot(app *backpack.App) error {
 		if err := p.wireRealtime(app); err != nil {
 			return err
 		}
+		if err := p.wireSearch(app); err != nil {
+			return err
+		}
 		if err := p.registerChat(app); err != nil {
 			return err
 		}