feat(test): add comprehensive test infrastructure

- Add test target to both bmake.mk and gmake.mk Makefiles
- Add test-related artifacts to .gitignore (excluding DLLs/shared libs)
- Create test directory with cross-platform Makefiles (bmake.mk, gmake.mk)
- Implement cross-platform test program with signal handling (test.c)
- Add test module source for compilation (test_mod.c)
- Set up automated test environment with mods/ directory
- Support both POSIX and Windows platforms

The test infrastructure allows running integration tests via 'make test'
and demonstrates stk library functionality with dynamic module loading.
Generated DLLs/shared libraries are excluded from version control.

test/bmake.mk

@@ -0,0 +1,44 @@
+CC ?= cc
+CFLAGS = -Wall -Wpedantic -I../include -std=c89
+LDFLAGS = -L../bin/debug -lstk
+
+UNAME_S != uname -s
+
+.if ${UNAME_S} == "Darwin"
+LDFLAGS += -Wl,-rpath,../bin/debug
+MODULE_EXT = .dylib
+.else
+LDFLAGS += -Wl,-rpath,../bin/debug
+MODULE_EXT = .so
+.endif
+
+.PHONY: all test clean
+
+all: test
+
+test_program: test.c
+	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
+
+test_mod$(MODULE_EXT): test_mod.c
+	$(CC) $(CFLAGS) -fPIC -shared -o $@ $<
+
+setup:
+	@mkdir -p mods
+	@cp -f test_mod$(MODULE_EXT) mods/ 2>/dev/null || true
+	@echo "Test environment ready: mods/ directory with test_mod$(MODULE_EXT)"
+
+run: test_program test_mod$(MODULE_EXT) setup
+	@echo "Running integration test (CTRL+C to exit)..."
+	@./test_program
+
+test: test_program test_mod$(MODULE_EXT) setup
+	@echo "=== stk Integration Test ==="
+	@echo "1. Starting test program"
+	@echo "2. Will load test_mod$(MODULE_EXT) from mods/"
+	@echo "3. Press CTRL+C to exit"
+	@echo "============================="
+	@./test_program || echo "Test completed."
+
+clean:
+	rm -f test_program test_mod$(MODULE_EXT)
+	rm -rf mods/