refactor ZED capture into modular camera class with env config

Extract camera lifecycle (open, warmup, grab, close) and
environment-based configuration into src/zed/camera.{h,cc}.
Thin main.cc now only handles the dora event loop.

Closes #2

CMakeLists.txt

@@ -16,12 +16,13 @@ find_package(OpenCV REQUIRED)
 link_directories(${dora_link_dirs})
 link_directories(${ZED_LIBRARY_DIR})
 
-add_executable(dora_zed main.cc ${node_bridge})
+add_executable(dora_zed src/main.cc src/zed/camera.cc ${node_bridge})
 add_dependencies(dora_zed Dora_cxx)
 
 target_include_directories(
     dora_zed
     PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/src
         ${dora_cxx_include_dir}
         ${dora_c_include_dir}
         ${ZED_INCLUDE_DIRS}