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_refcount_double_fail.c

@@ -10,6 +10,8 @@
  * library exit(1)s.
  */
 
+static int handled_status = 0;
+
 akerr_ErrorContext *validate(void)
 {
     PREPARE_ERROR(e);
@@ -31,6 +33,7 @@ akerr_ErrorContext *one_cycle(void)
     } CLEANUP {
     } PROCESS(e) {
     } HANDLE(e, AKERR_KEY) {
+	handled_status = e->status;
     } HANDLE(e, AKERR_VALUE) {
     } FINISH(e, false);
     return e;
@@ -42,7 +45,9 @@ int main(void)
     AKERR_CHECK(akerr_slots_in_use() == 0);
 
     for ( int i = 0; i < 32; i++ ) {
+	handled_status = 0;
 	(void)one_cycle();
+	AKERR_CHECK(handled_status == AKERR_KEY);
     }
 
     AKERR_CHECK(akerr_slots_in_use() == 0);