feat(shaders_lab): visual node editor (imgui-node-editor) + multi-source

- cpp/vendor/imgui-node-editor: vendorized thedmd/imgui-node-editor v0.9.4
- cpp/functions/gfx/dag_node_editor: new visual pipeline editor replacing dag_panel
- DagStep: source_ids[4] + editor_pos + editor_uid (multi-input support)
- DagNodeDef: num_inputs explicit; circle reclassified as Op
- dag_compile: N inputs per node, topological ordering preserved
- main: use node editor; destroy on shutdown
- patch imgui_extra_math.inl: guard operator*(float, ImVec2) for imgui >= 18955

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cpp/vendor/imgui-node-editor/misc/cmake-modules/FindScopeGuard.cmake

@@ -0,0 +1,17 @@
+if (TARGET ScopeGuard)
+    return()
+endif()
+
+set(_ScopeGuard_SourceDir ${IMGUI_NODE_EDITOR_ROOT_DIR}/external/ScopeGuard)
+set(_ScopeGuard_BinaryDir ${CMAKE_BINARY_DIR}/external/ScopeGuard)
+
+add_subdirectory(${_ScopeGuard_SourceDir} ${_ScopeGuard_BinaryDir})
+
+include(${CMAKE_ROOT}/Modules/FindPackageHandleStandardArgs.cmake)
+
+find_package_handle_standard_args(
+    ScopeGuard
+    REQUIRED_VARS
+        _ScopeGuard_SourceDir
+)
+

cpp/vendor/imgui-node-editor/misc/cmake-modules/Findgl3w.cmake

@@ -0,0 +1,17 @@
+if (TARGET gl3w)
+    return()
+endif()
+
+set(_gl3w_SourceDir ${IMGUI_NODE_EDITOR_ROOT_DIR}/external/gl3w)
+set(_gl3w_BinaryDir ${CMAKE_BINARY_DIR}/external/gl3w)
+
+add_subdirectory(${_gl3w_SourceDir} ${_gl3w_BinaryDir})
+
+include(${CMAKE_ROOT}/Modules/FindPackageHandleStandardArgs.cmake)
+
+find_package_handle_standard_args(
+    gl3w
+    REQUIRED_VARS
+        _gl3w_SourceDir
+)
+

cpp/vendor/imgui-node-editor/misc/cmake-modules/Findimgui.cmake

@@ -0,0 +1,17 @@
+if (TARGET imgui)
+    return()
+endif()
+
+set(_imgui_SourceDir ${IMGUI_NODE_EDITOR_ROOT_DIR}/external/imgui)
+set(_imgui_BinaryDir ${CMAKE_BINARY_DIR}/external/imgui)
+
+add_subdirectory(${_imgui_SourceDir} ${_imgui_BinaryDir})
+
+include(${CMAKE_ROOT}/Modules/FindPackageHandleStandardArgs.cmake)
+
+find_package_handle_standard_args(
+    imgui
+    REQUIRED_VARS
+        _imgui_SourceDir
+)
+

cpp/vendor/imgui-node-editor/misc/cmake-modules/Findimgui_node_editor.cmake

@@ -0,0 +1,49 @@
+if (TARGET imgui_node_editor)
+    return()
+endif()
+
+#set(_imgui_node_editor_SourceDir ${IMGUI_NODE_EDITOR_ROOT_DIR})
+#set(_imgui_node_editor_BinaryDir ${CMAKE_BINARY_DIR}/NodeEditor)
+
+#add_subdirectory(${_imgui_node_editor_SourceDir} ${_imgui_node_editor_BinaryDir})
+
+find_package(imgui REQUIRED)
+
+set(_imgui_node_editor_Sources
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/crude_json.cpp
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/crude_json.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_bezier_math.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_bezier_math.inl
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_canvas.cpp
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_canvas.cpp
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_canvas.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_canvas.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_extra_math.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_extra_math.inl
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_node_editor_api.cpp
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_node_editor_internal.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_node_editor_internal.inl
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_node_editor.cpp
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/imgui_node_editor.h
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}/misc/imgui_node_editor.natvis
+)
+
+add_library(imgui_node_editor STATIC
+    ${_imgui_node_editor_Sources}
+)
+
+target_include_directories(imgui_node_editor PUBLIC
+    ${IMGUI_NODE_EDITOR_ROOT_DIR}
+)
+
+target_link_libraries(imgui_node_editor PUBLIC imgui)
+
+source_group(TREE ${IMGUI_NODE_EDITOR_ROOT_DIR} FILES ${_imgui_node_editor_Sources})
+
+include(${CMAKE_ROOT}/Modules/FindPackageHandleStandardArgs.cmake)
+
+find_package_handle_standard_args(
+    imgui_node_editor
+    REQUIRED_VARS
+        IMGUI_NODE_EDITOR_ROOT_DIR
+)

cpp/vendor/imgui-node-editor/misc/cmake-modules/Findstb_image.cmake

@@ -0,0 +1,17 @@
+if (TARGET stb_image)
+    return()
+endif()
+
+set(_stb_image_SourceDir ${IMGUI_NODE_EDITOR_ROOT_DIR}/external/stb_image)
+set(_stb_image_BinaryDir ${CMAKE_BINARY_DIR}/external/stb_image)
+
+add_subdirectory(${_stb_image_SourceDir} ${_stb_image_BinaryDir})
+
+include(${CMAKE_ROOT}/Modules/FindPackageHandleStandardArgs.cmake)
+
+find_package_handle_standard_args(
+    stb_image
+    REQUIRED_VARS
+        _stb_image_SourceDir
+)
+