fix: improve functional test stability and CI reliability

- Fix parallel test execution conflicts by moving test files to build dir
- Improve error handling in ci-build.sh with proper exit codes
- Update test file paths for out-of-tree build compatibility
- Add test-files and test-logs to .gitignore
- Add clean-functional-tests target to Makefile.am

ci-build.sh

@@ -215,10 +215,20 @@ build_and_test() {
         cd "$build_dir"
 
         # shellcheck disable=SC2086
-        ../configure -C $features $extra_args
+        if ! ../configure -C $features $extra_args; then
+            echo "ERROR: configure failed"
+            exit 1
+        fi
 
-        $MAKE CC="${CC}"
-        $MAKE check-functional-parallel
+        if ! $MAKE CC="${CC}"; then
+            echo "ERROR: make failed"
+            exit 1
+        fi
+
+        if ! $MAKE check-functional-parallel; then
+            echo "ERROR: functional tests failed"
+            exit 1
+        fi
 
         ./profanity -v
         $MAKE clean