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_swallow.c

@@ -9,6 +9,7 @@
  */
 
 static int wrong_handler_fired = 0;
+static int swallowed_status = 0;
 
 akerr_ErrorContext *boom(void)
 {
@@ -24,6 +25,7 @@ akerr_ErrorContext *swallow_it(void)
     ATTEMPT {
 	CATCH(e, boom());
     } CLEANUP {
+	swallowed_status = (e != NULL) ? e->status : 0;
     } PROCESS(e) {
     } HANDLE(e, AKERR_KEY) {
 	wrong_handler_fired = 1; /* does not match AKERR_VALUE */
@@ -38,6 +40,7 @@ int main(void)
     akerr_ErrorContext *res = swallow_it();
 
     AKERR_CHECK(wrong_handler_fired == 0);
+    AKERR_CHECK(swallowed_status == AKERR_VALUE);
     AKERR_CHECK(res == NULL); /* released even though unhandled */
     AKERR_CHECK(akerr_slots_in_use() == 0);
     fprintf(stderr, "err_swallow ok\n");