feat: add fabric-bridge node for RDMA/inter-host MXL flow sharing

- New fabric-bridge node: initiator mode reads local MXL flow and
  transfers via Fabrics (RDMA/TCP); target mode receives remote data
  and commits to local MXL flow writer
- Add set_mxl_instance/get_mxl_instance to Node base class
- CMake option DMF_BUILD_FABRICS=OFF by default (needs libfabric)
- Target publishes target_info in status for out-of-band exchange
- Initiator receives target_info via config parameter

nodes/fabric-bridge/CMakeLists.txt

@@ -0,0 +1,28 @@
+cmake_minimum_required(VERSION 3.24 FATAL_ERROR)
+
+project(dmf-node-fabric-bridge VERSION 0.1.0 LANGUAGES CXX)
+
+find_package(fmt CONFIG REQUIRED)
+find_package(spdlog CONFIG REQUIRED)
+find_package(nlohmann_json CONFIG REQUIRED)
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(libfabric REQUIRED IMPORTED_TARGET libfabric)
+
+add_executable(dmf-node-fabric-bridge
+    src/fabric_bridge_node.cpp
+    src/main.cpp
+)
+
+target_link_libraries(dmf-node-fabric-bridge PRIVATE
+    dmf-node
+    mxl-fabrics-objects
+    mxl-fabrics-headers
+    PkgConfig::libfabric
+    spdlog::spdlog
+    fmt::fmt
+    nlohmann_json::nlohmann_json
+)
+
+target_include_directories(dmf-node-fabric-bridge PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}/src
+)