Add admin template deletion with broadcast to all hosts

- DELETE /v1/admin/templates/{name} endpoint (admin-only)
- Broadcasts DeleteSnapshot RPC to all online hosts before removing DB record
- Frontend admin templates page uses deleteAdminTemplate() instead of
  team-scoped deleteSnapshot()
- Delete button shown for all template types, not just snapshots

internal/api/server.go

@@ -67,7 +67,7 @@ func New(
 	auditH := newAuditHandler(auditSvc)
 	statsH := newStatsHandler(statsSvc)
 	metricsH := newSandboxMetricsHandler(queries, pool)
-	buildH := newBuildHandler(buildSvc, queries)
+	buildH := newBuildHandler(buildSvc, queries, pool)
 
 	// OpenAPI spec and docs.
 	r.Get("/openapi.yaml", serveOpenAPI)
@@ -178,6 +178,7 @@ func New(
 		r.Use(requireAdmin(queries))
 		r.Put("/teams/{id}/byoc", teamH.SetBYOC)
 		r.Get("/templates", buildH.ListTemplates)
+		r.Delete("/templates/{name}", buildH.DeleteTemplate)
 		r.Post("/builds", buildH.Create)
 		r.Get("/builds", buildH.List)
 		r.Get("/builds/{id}", buildH.Get)