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_handle_dispatch.c

@@ -9,6 +9,7 @@
 static int a_fired = 0;
 static int b_fired = 0;
 static int c_fired = 0;
+static int b_status = 0;
 
 akerr_ErrorContext *boom(void)
 {
@@ -29,12 +30,14 @@ int main(void)
 	a_fired = 1;
     } HANDLE(e, AKERR_TYPE) {
 	b_fired = 1;
+	b_status = e->status;
     } HANDLE(e, AKERR_IO) {
 	c_fired = 1;
     } FINISH_NORETURN(e);
 
     AKERR_CHECK(a_fired == 0);
     AKERR_CHECK(b_fired == 1);
+    AKERR_CHECK(b_status == AKERR_TYPE);
     AKERR_CHECK(c_fired == 0);
     AKERR_CHECK(akerr_slots_in_use() == 0);
     fprintf(stderr, "err_handle_dispatch ok\n");