H2: E157 module CEIDs + server-side emission

Adds the canonical E157 collection-event identifiers in the 1570+ block:

  1570 ModuleProcessStateChange  (generic; fired on any transition)
  1571 ModuleNotExecuting
  1572 ModuleGeneralExecuting
  1573 ModuleStepExecuting
  1574 ModuleStepCompleted

Server installs a state-change handler that fires both the generic
CEID and the state-specific one for each transition.  Hosts that
prefer "wake me on any module change and I'll fan it out myself" can
subscribe to only the generic CEID; hosts that want narrower
notifications subscribe to specific states.

Closes Tranche H — E157 Module Process Tracking end-to-end (FSM +
Store + CEIDs + server emission).

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

include/secsgem/gem/e157_constants.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <cstdint>
+
+// E157 §6 standard collection-event identifiers, one per module state.
+// Equipment fires the matching CEID when a module transitions; hosts
+// subscribe via the standard S2F33 / S2F35 / S2F37 path.
+namespace secsgem::gem::e157 {
+
+inline constexpr uint32_t kCeidModuleProcessStateChange = 1570;
+inline constexpr uint32_t kCeidModuleNotExecuting       = 1571;
+inline constexpr uint32_t kCeidModuleGeneralExecuting   = 1572;
+inline constexpr uint32_t kCeidModuleStepExecuting      = 1573;
+inline constexpr uint32_t kCeidModuleStepCompleted      = 1574;
+
+}  // namespace secsgem::gem::e157