fix(server): make CURL optional for replay_http_server target

find_package(CURL REQUIRED) made libcurl-dev a hard configure-time dependency
for any build with DFLASH27B_TESTS=ON, even though the rest of the build
(dflash_server, server unit tests) already gates its own curl usage. Hosts
without libcurl-dev that previously configured cleanly now fail.

Drop REQUIRED and skip the replay_http_server target when CURL is not found.
The pytest driver checks for the binary and self-skips.

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

Author: easel

server/CMakeLists.txt

@@ -884,8 +884,13 @@ if(DFLASH27B_TESTS)
     if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/replay_http_server.cpp")
         # http_server.cpp #includes <curl/curl.h> for its upstream-proxy
         # passthrough; replay_http_server compiles that TU so it must link
-        # libcurl even though the stub backend itself doesn't use it.
-        find_package(CURL REQUIRED)
+        # libcurl even though the stub backend itself doesn't use it. Skip
+        # the target on hosts without libcurl-dev rather than fail configure
+        # — the rest of the build (server unit tests, dflash_server, etc.)
+        # has its own CURL gating and shouldn't be blocked by the test rig.
+        find_package(CURL)
+    endif()
+    if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/replay_http_server.cpp" AND CURL_FOUND)
         add_executable(replay_http_server
             test/replay_http_server.cpp
             test/scenario_store.cpp