LoRa Scanner: a MeshCore preset, and its packets read

- MeshCore joins the presets (EU/UK Narrow: 869.618 MHz, 62.5 kHz, SF8,
  CR 4/8, sync 0x12), after the Meshtastic ones so stored choices keep
  their number; `lora preset MeshCore` on the console
- lib/meshcore reads what MeshCore sends in clear: header, path, and a
  node's advert (name, kind, key, position)
- the list row, the details, a Capture's viewer and the console echo read
  a packet by the sync word it was received on
- the bandwidth is printed as 62.5, not 62

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

site/data/keys.toml

@@ -206,7 +206,7 @@ title = "LoRa Scanner, the packets"
 rows = [
     ["; .", "up, down"],
     ["Enter", "the packet's details"],
-    ["p", "pick a Meshtastic preset"],
+    ["p", "pick a preset"],
     ["c", "start a Capture, or stop it"],
     ["Tab", "the Sweep"],
 ]