Expand error status test coverage

- Added explicit status validation across error handling tests.
- Added lifecycle and slot-leak checks to older tests.
- Improved unhandled-error propagation coverage.
- Added repository guidance and a test runner script.
- Verified all 23 CTest tests pass.

Co-Authored by Codex GPT 5.4

tests/err_cleanup.c

@@ -1,4 +1,5 @@
 #include "akerror.h"
+#include "err_capture.h"
 
 int x;
 
@@ -34,10 +35,15 @@ int main(void)
     } CLEANUP {
     } PROCESS(errctx) {
     } HANDLE(errctx, AKERR_NULLPOINTER) {
+	AKERR_CHECK_STATUS(errctx, AKERR_NULLPOINTER);
 	if ( x == 0 ) {
-	    fprintf(stderr, "Cleanup works\n");
-	    return 0;
+	    akerr_log_method("Cleanup works\n");
+	} else {
+	    return 1;
 	}
-	return 1;
     } FINISH_NORETURN(errctx);
+
+    AKERR_CHECK(akerr_slots_in_use() == 0);
+    fprintf(stderr, "err_cleanup ok\n");
+    return 0;
 }