chore(cleanup): purge /command residuals — fakeEngine, canon golden, openapi

Follow-up tidy after the cross-service /command removal (#73):

- Rename the router test double dummyExecutor -> fakeEngine (and the
  newExecutor / setupRouterExecutor helpers -> newFakeEngine /
  setupRouterEngine): it implements handler.Engine now, "executor" was a
  leftover of the removed adapter. Test-only.

- Regenerate the ui/core canon signing golden onto user.games.order
  (request_user_games_command.json -> request_user_games_order.json, fresh
  canonical bytes + Ed25519 signature) and drop the last
  user.games.command references from the Go/TS tests and docs.

- Align game openapi: CommandRequest.cmd no longer carries minItems: 1. It
  is now used only by PUT /api/v1/order, which accepts an empty batch
  (clearing the player's stored order, equivalent to removing every
  command); the contract test freezes the empty-allowed shape.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

ui/PLAN.md

@@ -469,7 +469,7 @@ Acceptance criteria:
 
 - canonical-bytes output matches gateway-side output byte-for-byte
   for the three Phase-3 message types (`user.account.get`,
-  `lobby.my.games.list`, `user.games.command`);
+  `lobby.my.games.list`, `user.games.order`);
 - a request signed by `ui/core` is accepted by the gateway's own
   verifier in a unit test (`TestParityRequestSignedByUICoreAcceptedByGateway`);
 - a response signed by `gateway/authn`'s `Ed25519ResponseSigner` is
@@ -648,7 +648,7 @@ Acceptance criteria (met):
   KB measured);
 - `WasmCore.signRequest` produces canonical bytes byte-for-byte
   identical to the gateway-side fixtures for three message types
-  (`request_user_account_get`, `request_user_games_command`,
+  (`request_user_account_get`, `request_user_games_order`,
   `request_lobby_my_games_list`);
 - `WasmCore` exposes the same `Core` TypeScript types future
   `WailsCore` and `CapacitorCore` adapters will satisfy.

ui/core/README.md

@@ -130,7 +130,7 @@ The `canon` test suite combines:
 - byte-equality on golden JSON fixtures under
   `canon/testdata/` for three request types
   (`user.account.get`, `lobby.my.games.list`,
-  `user.games.command`), one response (`ok`), and one event
+  `user.games.order`), one response (`ok`), and one event
   (`gateway.server_time`);
 - mutation tests proving every signed field is bound into the
   signature;

ui/core/canon/request_test.go

@@ -71,7 +71,7 @@ func TestBuildRequestSigningInputChangesWhenSignedFieldChanges(t *testing.T) {
 	base := canon.RequestSigningFields{
 		ProtocolVersion: "v1",
 		DeviceSessionID: "device-session-123",
-		MessageType:     "user.games.command",
+		MessageType:     "user.games.order",
 		TimestampMS:     123456789,
 		RequestID:       "request-123",
 		PayloadHash:     sha256Sum([]byte("payload")),
@@ -143,7 +143,7 @@ func TestRequestCanonicalBytesFixtures(t *testing.T) {
 	fixtures := []string{
 		"request_user_account_get.json",
 		"request_lobby_my_games_list.json",
-		"request_user_games_command.json",
+		"request_user_games_order.json",
 	}
 
 	for _, name := range fixtures {

ui/core/canon/signature_test.go

@@ -22,7 +22,7 @@ func TestVerifyRequestSignature(t *testing.T) {
 	fields := canon.RequestSigningFields{
 		ProtocolVersion: "v1",
 		DeviceSessionID: "device-session-123",
-		MessageType:     "user.games.command",
+		MessageType:     "user.games.order",
 		TimestampMS:     123456789,
 		RequestID:       "request-123",
 		PayloadHash:     sha256Sum([]byte("payload")),

ui/core/canon/testdata/request_user_games_order.json

@@ -1,13 +1,13 @@
 {
-  "message_type": "user.games.command",
+  "message_type": "user.games.order",
   "protocol_version": "v1",
   "device_session_id": "device-session-1",
   "timestamp_ms": 1700000001000,
   "request_id": "req-games-1",
   "payload": "games-payload",
   "payload_hash_hex": "a8322c99bf424939cd3a1e5a41b5edb67e567bff87c49e8ff229be60976960e0",
-  "expected_canonical_bytes_hex": "1167616c6178792d726571756573742d7631027631106465766963652d73657373696f6e2d3112757365722e67616d65732e636f6d6d616e640000018bcfe56be80b7265712d67616d65732d3120a8322c99bf424939cd3a1e5a41b5edb67e567bff87c49e8ff229be60976960e0",
+  "expected_canonical_bytes_hex": "1167616c6178792d726571756573742d7631027631106465766963652d73657373696f6e2d3110757365722e67616d65732e6f726465720000018bcfe56be80b7265712d67616d65732d3120a8322c99bf424939cd3a1e5a41b5edb67e567bff87c49e8ff229be60976960e0",
   "private_key_seed_hex": "0303030303030303030303030303030303030303030303030303030303030303",
   "public_key_base64": "7UkoxijRwsbq6QM4kFmVYSlZJzpcY/k2NsFGFKyHN9E=",
-  "expected_signature_hex": "262d5480451560d9b2ca96468b0e962e4288eabb4dff29dbc66c491a37dd92b779d2b89853083a695317f8535e49c402dcfd49a11fd2926f3af42ceb745e2b0a"
+  "expected_signature_hex": "b4a9a1eb2eb67777469d87ed7c513afd89f0c0a96ca9e0d945cd327830c11a7834ac073f6a872d8121cd7674b9491399a0256210292615bd424d11d0db37200c"
 }

ui/frontend/tests/wasm-core-canon-parity.test.ts

@@ -79,7 +79,7 @@ beforeAll(async () => {
 describe("WasmCore canon parity with gateway fixtures", () => {
 	test.each([
 		"request_user_account_get.json",
-		"request_user_games_command.json",
+		"request_user_games_order.json",
 		"request_lobby_my_games_list.json",
 	])("%s — canonical bytes byte-for-byte equal", (name) => {
 		const fixture = readJson<RequestFixture>(name);