refactor(cmake): de-churn batches A-E (fork-cleanup doc 02)

- KICAD_WASM_LAYER cache var replaces 25 ${CMAKE_SOURCE_DIR}/../wasm reach-outs
- pcbnew Python install: wrap-and-reindent -> early-return guard
- list(REMOVE_ITEM) for PCBNEW_IO_LIBRARIES (cache-FORCE), eeschema importers, GAL_SRCS
- add_shader redefined via wasm/cmake/WasmShaderOverride.cmake (upstream calls reused)
- additive BUILD_KIWAY_DLL property overrides; api kiapi type var
- pcb_calculator whole-file fork -> wasm block + guarded native body

Upstream-byte-identical where possible. WASM build + e2e (9/9, -O1) verified.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

kicad

@@ -1 +1 @@
-Subproject commit a2c634f2f5f061ce13dc09fae3801c618f2a9f81
+Subproject commit b5ac6dcbe40defcfa21938de80cd6d4ce3a23711

wasm/cmake/WasmShaderOverride.cmake

@@ -0,0 +1,56 @@
+# WASM shader override.
+#
+# Redefines add_shader() to convert GLSL 1.20 -> GLSL ES 3.0 before embedding the shader as a
+# C++ string, so common/gal/CMakeLists.txt's unconditional add_shader() calls produce ES3
+# shaders on Emscripten while native keeps the upstream GLSL-1.20 path. The later definition
+# wins, so this file must be include()d AFTER upstream's add_shader() definition and BEFORE the
+# add_shader() calls. (Same conversion as tests/gal-regression/wasm/generate_shaders.py.)
+#
+# include()d (not add_subdirectory'd) from common/gal/CMakeLists.txt, so ${CMAKE_CURRENT_SOURCE_DIR}
+# / ${CMAKE_CURRENT_BINARY_DIR} below resolve to that directory, exactly as the inline fork did.
+
+find_program( PYTHON3_EXECUTABLE python3 REQUIRED )
+
+function( add_shader outTarget inFile shaderName )
+    # Determine shader type from filename
+    string(FIND "${inFile}" "frag" _is_frag)
+    if(_is_frag GREATER -1)
+        set(SHADER_TYPE "fragment")
+    else()
+        set(SHADER_TYPE "vertex")
+    endif()
+
+    set(es3GlslFile "${CMAKE_CURRENT_BINARY_DIR}/${shaderName}_es3.glsl")
+    set(outCppName "${shaderName}.cpp")
+    set(outHeaderName "${shaderName}.h")
+
+    # Step 1: Convert GLSL 120 -> ES 3.0
+    add_custom_command(
+        OUTPUT ${es3GlslFile}
+        COMMAND ${PYTHON3_EXECUTABLE}
+            ${CMAKE_CURRENT_SOURCE_DIR}/shaders/convert_glsl_es3.py
+            ${CMAKE_CURRENT_SOURCE_DIR}/shaders/${inFile}
+            ${es3GlslFile}
+            ${SHADER_TYPE}
+        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/shaders/${inFile}
+                ${CMAKE_CURRENT_SOURCE_DIR}/shaders/convert_glsl_es3.py
+    )
+
+    # Step 2: Embed as C++ string (same as native path)
+    add_custom_command(
+        OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${outCppName}
+               ${CMAKE_BINARY_DIR}/include/gal/shaders/${outHeaderName}
+        COMMAND ${CMAKE_COMMAND}
+            -DSOURCE_FILE="${es3GlslFile}"
+            -DOUT_CPP_DIR="${CMAKE_CURRENT_BINARY_DIR}/"
+            -DOUT_HEADER_DIR="${CMAKE_BINARY_DIR}/include/gal/shaders/"
+            -DOUT_CPP_FILENAME="${outCppName}"
+            -DOUT_HEADER_FILENAME="${outHeaderName}"
+            -DOUT_VAR_NAME="${shaderName}"
+            -P ${KICAD_CMAKE_MODULE_PATH}/BuildSteps/CreateShaderCpp.cmake
+        DEPENDS ${es3GlslFile}
+    )
+
+    target_sources( ${outTarget} PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/${outCppName} )
+    target_include_directories( ${outTarget} PUBLIC ${CMAKE_BINARY_DIR}/include/gal/shaders/ )
+endfunction()