Last three follow-ups from the post-release backlog, one commit each. Independent of #11282, #11283, #11284 and #11285; all five branch from develop and merge cleanly in any order.

• resetRadioConfig() installs the default channels, which carry the public PSK, but only loadFromDisk() sanitized them. When the channel file is absent or corrupt that call is a no-op (channels_count is 0), so a first boot or factory reset of a ham-only board could transmit encrypted on ham allocations until the next boot. Now stripped again right after initDefaults(), before onConfigChanged() publishes hashes.
• lastPortNumToRadio was written for every portnum a client sent, but only traceroute, position, waypoint, alert, telemetry and text are ever read back. A client cycling portnums grew the map without bound; it now records only those six.
• payload.bytes is not NUL-terminated, and two readers scanned past the received size into whatever the previous occupant of the pooled packet left behind: MessageStore::addFromPacket bounded strnlen only by MAX_MESSAGE_SIZE, and DropzoneModule compared strlen(matchCompare) bytes regardless of payload.size. Both are now bounded by the received size. In-field reads, so no OOB, but they leaked stale bytes into stored text and into a match decision. The two sprintf calls there became snprintf while in the area.

Item 18 from the backlog (splitting manually-verified from XEdDSA signer provenance in the warm store) needs no change: d6b12ea already added WarmProtected::XeddsaSigner alongside the independent signer bit, so the two are distinguished.

Summary by CodeRabbit

• Bug Fixes
  • Prevented message processing from reading beyond the received payload.
  • Improved handling of configuration resets on licensed devices, preserving the correct operating settings.
  • Prevented excessive resource usage caused by unsupported packet types.
  • Strengthened received-message matching to safely handle payloads that are not null-terminated.