fix(daemon)+fix(client): close four fool-proofing gaps

C++ (equipment_service.hpp):
- ReportSubstrate ARRIVED: check CreateResult and return INVALID_OBJECT
  when the substrate ID already exists, instead of silently doing nothing
- ReportSubstrate/ReportModule default switch branches: return false
  (→ CANNOT_DO_NOW) for unknown enum values instead of silently accepting

Python (_client.py):
- @eq.command: raise NameError (client-side name validation) instead of
  SecsGemError (which means "daemon declined a request") — wrong type
- Module docstring: update example to show @eq.command / eq.names API

Test (test_daemon_service.cpp):
- Add duplicate-ARRIVED check (expects INVALID_OBJECT)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

include/secsgem/daemon/equipment_service.hpp

@@ -536,7 +536,8 @@ class EquipmentService final : public pb::Equipment::Service {
     auto outcome = rt_.read_sync([this, sid, cid, slot, m]() -> std::optional<bool> {
       auto& subs = rt_.model().substrates;
       if (m == pb::SubstrateReport::ARRIVED) {
-        subs.create(sid, cid, slot);  // AtSource / NeedsProcessing
+        if (subs.create(sid, cid, slot) == gem::SubstrateStore::CreateResult::Denied_AlreadyExists)
+          return std::nullopt;  // → INVALID_OBJECT: duplicate substrate ID
         return true;
       }
       if (!subs.has(sid)) return std::nullopt;
@@ -550,7 +551,7 @@ class EquipmentService final : public pb::Equipment::Service {
         case pb::SubstrateReport::PROCESSED:
           return subs.fire_processing_event(sid, gem::SubstrateProcessingEvent::EndProcessing);
         default:
-          return true;
+          return false;  // unknown milestone
       }
     });
     ack_from_outcome(outcome, resp, "substrate '" + sid + "'",
@@ -575,7 +576,7 @@ class EquipmentService final : public pb::Equipment::Service {
         case pb::ModuleReport::NOT_EXECUTING:
           return mods.fire(mid, gem::ModuleEvent::Reset);
         default:
-          return true;
+          return false;  // unknown state
       }
     });
     // Module auto-creates, so "not found" can't happen; only the FSM verdict.