feat: About dialog with version, commit, build time and settings path

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

cmake/write_build_info.cmake

@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: MIT
+#
+# Writes ${OUT} with the three strings src/build_info.hpp declares. Run both at
+# configure time (so the file exists when add_executable names it) and on every
+# build (so the commit and the timestamp are the ones that produced the binary).
+#
+# Expects: SRC (the source tree), OUT (the .cpp to write), VERSION.
+
+set(COMMIT "unknown")
+find_package(Git QUIET)
+if(GIT_FOUND AND EXISTS "${SRC}/.git")
+  execute_process(
+    COMMAND ${GIT_EXECUTABLE} describe --always --dirty
+    WORKING_DIRECTORY "${SRC}"
+    OUTPUT_VARIABLE GIT_OUT
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+    ERROR_QUIET
+    RESULT_VARIABLE GIT_RC)
+  if(GIT_RC EQUAL 0 AND NOT GIT_OUT STREQUAL "")
+    set(COMMIT "${GIT_OUT}")
+  endif()
+endif()
+
+string(TIMESTAMP STAMP "%Y-%m-%d %H:%M UTC" UTC)
+
+file(WRITE "${OUT}"
+"// SPDX-License-Identifier: MIT
+// Generated by cmake/write_build_info.cmake. Do not edit, do not commit.
+#include \"build_info.hpp\"
+
+namespace udpscope::build_info {
+
+const char* const kVersion = \"${VERSION}\";
+const char* const kCommit = \"${COMMIT}\";
+const char* const kTimestamp = \"${STAMP}\";
+
+}  // namespace udpscope::build_info
+")