Space multi-line command replies MESH_MULTI_SEND_DELAY_MS apart (v0.21.5)

Production incident: '#rss get lublin' returned an array of lines and
CommandService sent each one back-to-back within the same second — on the real
mesh 3 of 4 items were dropped in RF (the owner saw only the last one).

CommandService.onRx now waits MESH_MULTI_SEND_DELAY_MS (new env, default 5000 =
5 s, read at construction like the other timing knobs) between consecutive
lines of an array reply — no delay before the first line. The delay sits in the
shared per-line loop, so both the respond() path and the legacy sendText
fallback are covered by one await.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mesh-bot",
-  "version": "0.21.4",
+  "version": "0.21.5",
   "description": "",
   "author": "",
   "private": true,