fix(server): link prompt_normalize.cpp into replay_http_server

http_server.cpp now calls normalize_system_for_cache (added to main
during billing-header strip work). The replay_http_server test target
was missing the .cpp that defines it.

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

Author: easel

server/CMakeLists.txt

@@ -891,7 +891,8 @@ if(DFLASH27B_TESTS)
             test/scenario_store.cpp
             test/stub_model_backend.cpp
             src/server/http_server.cpp
-            src/server/model_card.cpp)
+            src/server/model_card.cpp
+            src/server/prompt_normalize.cpp)
         target_include_directories(replay_http_server PRIVATE
             ${DFLASH27B_SRC_INCLUDE_DIRS}
             ${CMAKE_CURRENT_SOURCE_DIR}/test