A3: S12 Wafer Maps stream (E5 §13)

Adds the core map-management messages: setup send/request (F1-F4),
transmit inquire/grant (F5/F6), data send in row format (F7/F8), and
the one-way error report (F19).  Reference points (REFP) are an
external struct shared across F1 and F4.

The alternative data encodings — array format (F9/F10), coordinate
format (F11/F12), and the corresponding request pairs (F13-F18) —
are scope-deferred.  They're mechanical YAML edits once a tool needs
them; the codec already handles the underlying BINARY/list shapes.

Three new ack enums: MapSetupAck (SDACK), MapTransmitGrant (GRANT),
MapDataAck (MAPER).  No state machine yet — maps are a data exchange,
not a lifecycle.

secsgem-py ships S12F0-F19 as a single block; this commit covers the
practically-used subset and matches their wire shapes where they
overlap.

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

include/secsgem/gem/messages_helpers.hpp

@@ -140,4 +140,35 @@ enum class TerminalAck : uint8_t {  // S10F2, S10F4
   TerminalNotAvailable = 2,
 };
 
+// E5 §13 S12 (Wafer Maps).  Encoded as separate enums even though the
+// underlying byte semantics differ slightly across F2/F6/F8 — keeping
+// them distinct preserves call-site readability.
+// Reference point on a wafer/substrate map (E5 §13.7.4 REFP).  Declared
+// out of line so the messages.yaml catalog can mark it `external_struct`
+// and reuse the same C++ type across F1 / F4.
+struct ReferencePoint {
+  int32_t x;
+  int32_t y;
+};
+
+enum class MapSetupAck : uint8_t {  // S12F2 SDACK
+  Accept = 0,
+  Error  = 1,
+};
+
+enum class MapTransmitGrant : uint8_t {  // S12F6 GRANT
+  Granted             = 0,
+  BusyTryAgain        = 1,
+  NoSpaceAvailable    = 2,
+  DuplicateMID        = 3,
+  MaterialNotRecognized = 4,
+};
+
+enum class MapDataAck : uint8_t {  // S12F8 MAPER
+  Accept       = 0,
+  FormatError  = 1,
+  UnknownID    = 2,
+  AbortNoMap   = 3,
+};
+
 }  // namespace secsgem::gem