feat(imgui): embeddable plot widget and demo

adapters/glfw/CMakeLists.txt

@@ -1,44 +1,10 @@
 # The GLFW adapter: the reference host for the library. It owns the window, the
 # context and the loop, and translates GLFW's events into plot::input events.
 #
-# Dependency discovery follows the design spec's order: find_package first,
-# pkg-config next, FetchContent only when neither can supply GLFW (the last
-# resort, because it needs the network).
-set(plot_glfw_dep "")
-
-find_package(glfw3 3.3 QUIET)
-if(TARGET glfw)
-  set(plot_glfw_dep glfw)
-elseif(TARGET glfw3::glfw3)
-  set(plot_glfw_dep glfw3::glfw3)
-endif()
-
-if(NOT plot_glfw_dep)
-  find_package(PkgConfig QUIET)
-  if(PkgConfig_FOUND)
-    pkg_check_modules(GLFW_PC QUIET IMPORTED_TARGET glfw3)
-    if(TARGET PkgConfig::GLFW_PC)
-      set(plot_glfw_dep PkgConfig::GLFW_PC)
-    endif()
-  endif()
-endif()
-
-if(NOT plot_glfw_dep)
-  message(STATUS "plot: glfw3 not found via find_package or pkg-config; fetching it")
-  include(FetchContent)
-  set(GLFW_BUILD_DOCS OFF CACHE BOOL "" FORCE)
-  set(GLFW_BUILD_TESTS OFF CACHE BOOL "" FORCE)
-  set(GLFW_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
-  set(GLFW_INSTALL OFF CACHE BOOL "" FORCE)
-  FetchContent_Declare(glfw
-    GIT_REPOSITORY https://github.com/glfw/glfw.git
-    GIT_TAG 3.4
-    GIT_SHALLOW TRUE)
-  FetchContent_MakeAvailable(glfw)
-  set(plot_glfw_dep glfw)
-endif()
-
-message(STATUS "plot: GLFW adapter dependency: ${plot_glfw_dep}")
+# GLFW is resolved by the shared plot_find_glfw() (cmake/plot_options.cmake), so a
+# build that also enables the Dear ImGui adapter -- which needs GLFW for
+# imgui_impl_glfw -- discovers (and at worst fetches) a single copy.
+plot_find_glfw(plot_glfw_dep)
 
 add_library(plot_glfw STATIC glfw_host.cpp)
 add_library(plot::glfw ALIAS plot_glfw)