Docs Update for C++ [4/4] (Blackholio) (#4169)

# Description of Changes

In order to give reviewers a chance to finish in one session the docs
are getting split up for the C++ update. This pass contains the
following section update:
- Unity Blackholio Tutorial
- Unreal Blackholio Tutorial
- Added /demo/Blackholio/server-cpp

# API and ABI breaking changes

N/A

# Expected complexity level and risk

1 - Just documentation additions

# Testing

- [x] Manually tested each block

Author: JasonAtClockwork

demo/Blackholio/server-cpp/spacetimedb/.gitignore

@@ -0,0 +1,21 @@
+# Build directories
+/build/
+/build_*/
+
+# IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# OS generated files
+.DS_Store
+Thumbs.db
+
+# CMake cache
+CMakeCache.txt
+CMakeFiles/
+
+# Compiled WASM files
+*.wasm
+*.opt.wasm

demo/Blackholio/server-cpp/spacetimedb/CMakeLists.txt

@@ -0,0 +1,63 @@
+cmake_minimum_required(VERSION 3.20)
+project(spacetime_cpp_module LANGUAGES C CXX)
+
+# Set C++ standard
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# Set the module source file
+set(MODULE_SOURCE "src/lib.cpp" CACHE STRING "Source file for the SpacetimeDB module")
+
+# Export compile commands for better IDE support
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+# Set optimization level for Release builds
+if(CMAKE_BUILD_TYPE STREQUAL "Release")
+  set(CMAKE_CXX_FLAGS_RELEASE "-O2")
+endif()
+
+# ------------------------------------------------------------------------------
+# SpacetimeDB C++ SDK - Use local SDK from repository
+# ------------------------------------------------------------------------------
+
+set(SPACETIMEDB_CPP_SDK_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../../../../crates/bindings-cpp")
+message(STATUS "Using local SpacetimeDB C++ SDK: ${SPACETIMEDB_CPP_SDK_DIR}")
+add_subdirectory("${SPACETIMEDB_CPP_SDK_DIR}" "${CMAKE_BINARY_DIR}/_deps/spacetime_cpp_sdk-build")
+
+# Create the main module executable
+add_executable(lib ${MODULE_SOURCE})
+
+# Link against the SDK target (preferred alias)
+target_link_libraries(lib PRIVATE spacetimedb_cpp_library)
+
+# Configure Emscripten-specific settings for WASM output
+if(CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
+  set(EXPORTED_FUNCS "['_malloc','_free','___describe_module__','___call_reducer__','___call_view__','___call_view_anon__','___call_procedure__']")
+
+  # Compile options/defines for WASM
+  # (apply to both the module and the SDK, so everything sees the same feature flags)
+  target_compile_options(lib PRIVATE -fno-exceptions)
+  target_compile_options(spacetimedb_cpp_library PRIVATE -fno-exceptions)
+
+  # Uncomment the following to allow unstable features of SpacetimeDB
+  #target_compile_definitions(lib PRIVATE SPACETIMEDB_UNSTABLE_FEATURES)
+  #target_compile_definitions(spacetimedb_cpp_library PUBLIC SPACETIMEDB_UNSTABLE_FEATURES)
+
+  target_link_options(lib PRIVATE
+    "SHELL:-sSTANDALONE_WASM=1"
+    "SHELL:-sWASM=1"
+    "SHELL:--no-entry"
+    "SHELL:-sEXPORTED_FUNCTIONS=${EXPORTED_FUNCS}"
+    "SHELL:-sERROR_ON_UNDEFINED_SYMBOLS=1"
+    "SHELL:-sFILESYSTEM=0"
+    "SHELL:-sDISABLE_EXCEPTION_CATCHING=1"
+    "SHELL:-sALLOW_MEMORY_GROWTH=0"
+    "SHELL:-sINITIAL_MEMORY=16MB"
+    "SHELL:-sSUPPORT_LONGJMP=0"
+    "SHELL:-sSUPPORT_ERRNO=0"
+    "SHELL:-std=c++20"
+    "SHELL:-O2"
+  )
+
+  set_target_properties(lib PROPERTIES OUTPUT_NAME "lib" SUFFIX ".wasm")
+endif()