Add unit test suite and complete protocol documentation

- Add test framework (test.h) with assertion macros and test runner
- Add comprehensive unit tests (test_network.c) covering:
  - Packet parsing and error handling
  - User registration and authentication
  - Room operations (create, join, leave, delete, list)
  - Direct messaging functionality
  - Message broadcasting
  - Password hashing
- Update Makefile with 'make test' target
- Rewrite PROTOCOL file with complete specification:
  - All 14 packet types with data layouts
  - All error codes with descriptions
  - Typical usage flows

test.h

@@ -0,0 +1,53 @@
+/* Simple unit test framework for asfur */
+#ifndef TEST_H
+#define TEST_H
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int tests_run = 0;
+static int tests_passed = 0;
+static int tests_failed = 0;
+
+#define TEST_ASSERT(cond, msg) do { \
+	if (!(cond)) { \
+		printf("  FAIL: %s\n", msg); \
+		return 1; \
+	} \
+} while(0)
+
+#define TEST_ASSERT_EQ(a, b, msg) do { \
+	if ((a) != (b)) { \
+		printf("  FAIL: %s (expected %d, got %d)\n", msg, (int)(b), (int)(a)); \
+		return 1; \
+	} \
+} while(0)
+
+#define TEST_ASSERT_STR_EQ(a, b, msg) do { \
+	if (strcmp((a), (b)) != 0) { \
+		printf("  FAIL: %s (expected '%s', got '%s')\n", msg, (b), (a)); \
+		return 1; \
+	} \
+} while(0)
+
+#define RUN_TEST(test_fn) do { \
+	tests_run++; \
+	printf("Running %s...\n", #test_fn); \
+	if (test_fn() == 0) { \
+		printf("  PASS\n"); \
+		tests_passed++; \
+	} else { \
+		tests_failed++; \
+	} \
+} while(0)
+
+#define TEST_SUMMARY() do { \
+	printf("\n=== Test Summary ===\n"); \
+	printf("Total:  %d\n", tests_run); \
+	printf("Passed: %d\n", tests_passed); \
+	printf("Failed: %d\n", tests_failed); \
+	return tests_failed > 0 ? 1 : 0; \
+} while(0)
+
+#endif