slice 8C Phase B.2 + C.1/C.2: retire disk subsystem + rewire disk mgmt to agent

Retired (~12.3k LOC): internal/storage/* (scan/format/attach/migrate/safety),
backup restic/crossdrive/restore_drives/disk_layout/local_infra/restore_scan/
paths + restore_app, report/infra_backup*/infra_pull, setup/scanner,
monitor/watchdog+pinger, web/storage_handlers+handler_restore. Surgically split
backup.Manager to app-data only (DB dumps + volume tars + app restore; dropped
restic + cross-drive + snapshot history). Fixed router/main/web wiring.
Added agent-backed disk API (web/agent_disk_handlers.go): /api/disks list/
assign/eject/format proxying agentapi; data-bearing format refusal -> HTTP 409
'operator authorization required'. report/config_pull.go keeps the setup
fresh-install config download. go build + go test green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

controller/internal/web/handler_export.go

@@ -9,6 +9,23 @@ import (
 	"gitea.dooplex.hu/admin/felhom-controller/internal/appexport"
 )
 
+// jsonResponse writes a JSON body with a 200 status.
+// (Shared JSON helper previously defined in the now-removed storage_handlers.go.)
+func jsonResponse(w http.ResponseWriter, v interface{}) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	json.NewEncoder(w).Encode(v)
+}
+
+// jsonError writes a JSON error response with the given status code.
+func jsonError(w http.ResponseWriter, msg string, code int) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(code)
+	json.NewEncoder(w).Encode(map[string]interface{}{
+		"ok":    false,
+		"error": msg,
+	})
+}
+
 // ServeExportAPI dispatches /api/export/* endpoints.
 func (s *Server) ServeExportAPI(w http.ResponseWriter, r *http.Request) {
 	path := r.URL.Path