feat: add solution for smallest palindromic rearrangement ii

- add problem 3518 implementation
- add build configuration with debug and release modes
- add test cases and examples
- add makefile for problem-specific build workflow

Makefile

@@ -0,0 +1,45 @@
+export ROOT_DIR := $(CURDIR)
+
+export BUILD_ROOT := $(ROOT_DIR)/build
+
+export CC = gcc
+export LDFLAGS = -lstdc++
+
+BUILD_TYPE ?= Release
+
+ifeq ($(BUILD_TYPE),Debug)
+	export CFLAGS = -std=c++23 -Wall -Wextra -Werror -Wpedantic -g -O0
+else ifeq ($(BUILD_TYPE),Release)
+	export CFLAGS = -std=c++23 -Wall -Wextra -Werror -Wpedantic -O2
+else
+	$(error Unknown BUILD_TYPE: $(BUILD_TYPE))
+endif
+
+
+.PHONY: all clean build run test rebuild
+
+all:
+ifndef PROBLEM_ID
+	$(error PROBLEM_ID is not set)
+endif
+	$(MAKE) -C $(PROBLEM_ID)
+
+clean:
+	rm -rf $(BUILD_ROOT)
+
+# NOTE: Examples
+# make build PROBLEM_ID=3518 BUILD_TYPE=Debug
+# make build PROBLEM_ID=3518
+build:
+	mkdir -p $(BUILD_ROOT)/$(PROBLEM_ID)
+	$(MAKE) -C $(PROBLEM_ID) build
+
+run:
+	$(MAKE) -C $(PROBLEM_ID) run
+
+test:
+	$(MAKE) -C $(PROBLEM_ID) test
+
+rebuild:
+	$(MAKE) -C $(PROBLEM_ID) clean
+	$(MAKE) -C $(PROBLEM_ID) build