CI: Add formatting validation steps

The following scripts are added to GitHub Actions workflow:
- check-format.sh to validate C/C++ and shell script formatting
- check-newline.sh to ensure files end with newline

Close #33

Author: jserv

.ci/check-format.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -u -o pipefail
+
+ret=0
+
+# Check C/C++ files with clang-format
+while IFS= read -r -d '' file; do
+    clang-format-18 -n --Werror "${file}" || ret=1
+done < <(git ls-files -z '*.c' '*.cpp' '*.h' ':!:*/submodule/*')
+
+# Check shell scripts with shfmt
+while IFS= read -r file; do
+    diff <(cat "${file}") <(shfmt -i 4 -bn -ci -sr "${file}")
+    if [ $? -ne 0 ]; then
+        echo "${file}" "mismatch"
+        ret=1
+    fi
+done < <(git ls-files '*.sh')
+
+exit ${ret}

.ci/check-newline.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+set -e -u -o pipefail
+
+ret=0
+show=0
+# Reference: https://medium.com/@alexey.inkin/how-to-force-newline-at-end-of-files-and-why-you-should-do-it-fdf76d1d090e
+while IFS= read -rd '' f; do
+    if file --mime-encoding "$f" | grep -qv binary; then
+        tail -c1 < "$f" | read -r _ || show=1
+        if [ $show -eq 1 ]; then
+            echo "Warning: No newline at end of file $f"
+            ret=1
+            show=0
+        fi
+    fi
+done < <(git ls-files -z app kernel lib arch include)
+
+exit $ret