refactor: restructure core module into domain-driven packages with 2672 insertions and 2220 deletions

Splits monolithic core module into bounded contexts: identity, billing, and notification domains. Moves entity definitions, repository interfaces, and service implementations into separate packages. Updates import paths across 25 files to align with new package structure. Removes cross-domain coupling by extracting shared value objects into a common package.

.backup.1.main.h

@@ -0,0 +1,51 @@
+#ifndef RLIB_MAIN
+#define RLIB_MAIN
+#include "rhttp.h"
+#include "rmerge.h"
+#include "rcov.h"
+#include "rcase.h"
+
+void forward_argument(int *argcc, char *argv[]) {
+    int argc = *argcc;
+    for (int i = 0; i < argc; i++) {
+        argv[i] = argv[i + 1];
+    }
+    argc--;
+    *argcc = argc;
+}
+
+int rlib_main(int argc, char *argv[]) {
+
+    if (argc == 1) {
+        printf("rlib\n\n");
+        printf("options:\n");
+        printf(" httpd - a http file server. Accepts port as argument.\n");
+        printf(" rmerge - a merge tool. Converts c source files to one file \n"
+               "          with local includes by giving main file as argument.\n");
+        printf(" rcov - coverage tool theat cleans up after himself. Based on "
+               "lcov.\n");
+        printf(" rcase - tool to swap input file automatically between"
+               "         camel case and snake case.\n");
+        return 0;
+    }
+
+    forward_argument(&argc, argv);
+
+    if (!strcmp(argv[0], "httpd")) {
+
+        return rhttp_main(argc, argv);
+    }
+    if (!strcmp(argv[0], "rmerge")) {
+        return rmerge_main(argc, argv);
+    }
+    if (!strcmp(argv[0], "rcov")) {
+        return rcov_main(argc, argv);
+    }
+    if (!strcmp(argv[0], "rcase")) {
+        return rcase_main(argc, argv);
+    }
+
+    return 0;
+}
+
+#endif