fix(api,panel): refuse file operations on a server without a world volume (#58)

Live: the files page against a server whose world claim does not exist (never
started, or reaped) created a Job whose Pod stayed Pending on
FailedScheduling (persistentvolumeclaim not found) until the executor's 90s
wait expired — a 90s spinner answered by a misleading 504 files_timeout, for
a request that is knowably impossible. Backup and restore have refused this
shape with 409 no_world_volume since the #42 round; the file routes now run
the same gate before any Job is created, and the panel maps the code to a
localized message (it previously fell back to the English server text).

panel/src/lib/api.ts

@@ -678,6 +678,8 @@ export function humanizeError(e: unknown): string {
       return t("no_backup");
     case "not_stopped":
       return t("not_stopped");
+    case "no_world_volume":
+      return t("no_world_volume");
     case "restore_unavailable":
       return t("restore_unavailable");
     default: