Add BR2_EXTERNAL skeleton

package/my-common-tool/Config.in

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+config BR2_PACKAGE_MY_COMMON_TOOL
+	bool "my-common-tool"
+	select BR2_PACKAGE_MY_SHARED_LIB
+	help
+	  A command-line utility shared across multiple Raspberry Pi
+	  projects. Depends on my-shared-lib.
+
+	  Installs the 'my-common-tool' binary into /usr/bin on the target.
+
+	  https://github.com/your-org/my-common-tool

package/my-common-tool/my-common-tool.mk

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+################################################################################
+#
+# my-common-tool
+#
+################################################################################
+
+MY_COMMON_TOOL_VERSION = 1.0.0
+MY_COMMON_TOOL_SITE = https://github.com/your-org/my-common-tool.git
+MY_COMMON_TOOL_SITE_METHOD = git
+MY_COMMON_TOOL_LICENSE = MIT
+MY_COMMON_TOOL_LICENSE_FILES = LICENSE
+MY_COMMON_TOOL_DEPENDENCIES = my-shared-lib
+
+define MY_COMMON_TOOL_BUILD_CMDS
+	$(MAKE) $(TARGET_CONFIGURE_OPTS) -C $(@D)
+endef
+
+define MY_COMMON_TOOL_INSTALL_TARGET_CMDS
+	$(INSTALL) -D -m 0755 $(@D)/my-common-tool $(TARGET_DIR)/usr/bin/my-common-tool
+endef
+
+$(eval $(generic-package))

package/my-shared-lib/Config.in

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+config BR2_PACKAGE_MY_SHARED_LIB
+	bool "my-shared-lib"
+	help
+	  A shared library providing common functionality used across
+	  multiple Raspberry Pi projects.
+
+	  Installs libmyshared.so into /usr/lib on the target.
+
+	  https://github.com/your-org/my-shared-lib

package/my-shared-lib/my-shared-lib.mk

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+################################################################################
+#
+# my-shared-lib
+#
+################################################################################
+
+# IMPORTANT: Update this version and hash when upgrading the package.
+# The hash file (my-shared-lib.hash) should also be updated accordingly.
+MY_SHARED_LIB_VERSION = 1.0.0
+MY_SHARED_LIB_SITE = https://github.com/your-org/my-shared-lib.git
+MY_SHARED_LIB_SITE_METHOD = git
+MY_SHARED_LIB_LICENSE = MIT
+MY_SHARED_LIB_LICENSE_FILES = LICENSE
+MY_SHARED_LIB_INSTALL_STAGING = YES
+
+# CMake options passed to the package's build.
+# Add any project-specific CMake definitions here.
+MY_SHARED_LIB_CONF_OPTS = \
+	-DBUILD_TESTS=OFF \
+	-DBUILD_EXAMPLES=OFF
+
+$(eval $(cmake-package))