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_break_variants.c

@@ -63,26 +63,26 @@ int main(void)
     akerr_ErrorContext *r;
 
     r = zero_break(0);
-    AKERR_CHECK(r != NULL && r->status == AKERR_VALUE);
+    AKERR_CHECK_STATUS(r, AKERR_VALUE);
     r = akerr_release_error(r);
     AKERR_CHECK(zero_break(7) == NULL);
 
     r = nonzero_break(7);
-    AKERR_CHECK(r != NULL && r->status == AKERR_INDEX);
+    AKERR_CHECK_STATUS(r, AKERR_INDEX);
     r = akerr_release_error(r);
     AKERR_CHECK(nonzero_break(0) == NULL);
 
     r = always_break();
-    AKERR_CHECK(r != NULL && r->status == AKERR_IO);
+    AKERR_CHECK_STATUS(r, AKERR_IO);
     r = akerr_release_error(r);
 
     r = zero_return(0);
-    AKERR_CHECK(r != NULL && r->status == AKERR_KEY);
+    AKERR_CHECK_STATUS(r, AKERR_KEY);
     r = akerr_release_error(r);
     AKERR_CHECK(zero_return(7) == NULL);
 
     r = nonzero_return(7);
-    AKERR_CHECK(r != NULL && r->status == AKERR_TYPE);
+    AKERR_CHECK_STATUS(r, AKERR_TYPE);
     r = akerr_release_error(r);
     AKERR_CHECK(nonzero_return(0) == NULL);