chore: allow building the embedded UI header separately (#1415)

Author: wbruna

examples/server/CMakeLists.txt

@@ -50,7 +50,13 @@ if(SD_SERVER_BUILD_FRONTEND AND EXISTS "${FRONTEND_DIR}")
 
         set_source_files_properties("${GENERATED_HTML_HEADER}" PROPERTIES GENERATED TRUE)
     else()
-        message(WARNING "pnpm not found, frontend build disabled")
+        if(EXISTS "${GENERATED_HTML_HEADER}")
+            message(STATUS "pnpm not found; using pre-built frontend header detected at ${GENERATED_HTML_HEADER}")
+            set(HAVE_FRONTEND_BUILD ON)
+            add_custom_target(${TARGET}_frontend)
+        else()
+            message(WARNING "pnpm not found; frontend build disabled.")
+        endif()
     endif()
 else()
     message(STATUS "Frontend disabled or directory not found: ${FRONTEND_DIR}")