L: E87 slot-map verification wire (S3F19/F20 + F21/F22)

Closes the slot-map verification gap I called out:

  S3F19 / F20  host -> equip: verify expected slot map against what
               the equipment has scanned. Equipment compares element-
               wise; on match drives CSMS NotRead -> Read and replies
               SVACK=Accept; on mismatch drives CSMS -> Mismatched and
               replies SVACK=Mismatch.

  S3F21 / F22  equip -> host: equipment-initiated slot map report
               (typically pushed after CARRIERID is confirmed).

New SVACK enum: SlotMapVerifyAck { Accept, Mismatch, CarrierUnknown,
Error }.  Server dispatch on S3F19 wires the actual CSMS transition
through the CarrierStore from D3.

Two round-trip tests cover both pairs; the FSM-driving behaviour is
exercised through the in-process tests because secs_server.cpp is
the dispatch entry point (no separate integration test needed beyond
the wire round-trip).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

include/secsgem/gem/messages_helpers.hpp

@@ -189,4 +189,13 @@ enum class PortGroupAck : uint8_t {
   Error  = 1,
 };
 
+// E87 slot-map verify ack code (SVACK).  Same byte used by S3F20
+// (verify reply) and S3F22 (host's ack of equipment's slot-map report).
+enum class SlotMapVerifyAck : uint8_t {
+  Accept       = 0,
+  Mismatch     = 1,
+  CarrierUnknown = 2,
+  Error        = 3,
+};
+
 }  // namespace secsgem::gem