[LifetimeSafety] False-negative in lifetimebound base class constructor

```cpp
struct T {};

struct S {
S(const T& t [[clang::lifetimebound]]);
};

struct S2 : S {
S2() : S(T{}) {} // Here S will outlive T{} but it does not trigger.
};
```
https://godbolt.org/z/WsnWzaEn6

Start with the reduced C++ reproducer in the issue and compare its behavior using the linked Compiler Explorer example. Trace the lifetimebound diagnostic handling for a base-class constructor call, then confirm that the shown temporary-lifetime case produces the expected warning without introducing diagnostics for valid code.

Written by the indexing model from the issue text.