ci: build: generate release version files for tags

Release binaries must be reproducible from the sources shipped with them.
Generate version and version.date from git when CI_COMMIT_TAG is set,
before the build reads either value.

Compute both values before writing either file, then print them for
traceability. The tag condition is the exact complement of the development
guard, so generation cannot run on development builds.

Assisted-by: codex:gpt-5.6-sol:medium-fast
Assisted-by: claude:opus-5:orchestrator
Signed-off-by: Petr Štetiar <petr.stetiar@prplfoundation.org>
References: PCF-2730

.gitlab/build.yml

@@ -52,6 +52,15 @@
         exit 1
       fi
 
+    - |
+      if [ -n "$CI_COMMIT_TAG" ]; then
+        release_version="$(scripts/getver.sh)"
+        release_version_date="$(scripts/get_source_date_epoch.sh)"
+        printf '%s\n' "$release_version" > version
+        printf '%s\n' "$release_version_date" > version.date
+        printf 'Generated release version data: version=%s version.date=%s\n' "$release_version" "$release_version_date"
+      fi
+
     - |
       if [ -z "$CI_COMMIT_TAG" ] && [ "$CI_DESIGNATED_BRANCH" != "$CI_COMMIT_BRANCH" ]; then
         echo "Enabling coredumps and exception tracing in the build."