phase 4: drop stale gRPC nomenclature from integration tests

Phase 4 replaced the gateway's authenticated edge listener with a
Connect-Go HTTP/h2c bootstrap that natively serves Connect, gRPC,
and gRPC-Web. Sweep the integration suite so test names, comments,
and helper docs match the new transport posture: rename
TestUserAccount_GetThroughGatewayGRPC to TestUserAccount_GetThroughGatewayEdge,
flip "authenticated gRPC" / "signed gRPC" / "gateway gRPC" comments
to "authenticated edge", and align testenv doc strings.

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

integration/testenv/clients.go

@@ -171,8 +171,8 @@ func (c *BackendInternalClient) Do(ctx context.Context, method, path string, bod
 // BackendUserClient hits backend's `/api/v1/user/*` endpoints
 // directly with `X-User-ID` set, mirroring what gateway does after
 // authenticated traffic verification. Used by scenarios whose
-// message_type is not registered in gateway's gRPC router (lobby
-// create, soft delete, etc.).
+// message_type is not registered in gateway's downstream router
+// (lobby create, soft delete, etc.).
 type BackendUserClient struct {
 	BaseURL string
 	UserID  string