Access all conversation IDs through the `ChatMemory` interface

Although this is possible through memory storage, I’m wondering if it would be possible to add a method to access all entry IDs (i.e., all conversation IDs) directly through the ChatMemory interface, to avoid injecting a ChatMemoryRepository

For example, in a RestController, I would have expected to be able to do the following:

private final ChatMemory chatMemory;

@GetMapping("/conversations")
public List<String> getConversations() {
    ResponseEntity.ok().body(chatMemory.getConversationIds());
}

Start by reading the ChatMemory interface and the ChatMemoryRepository boundary mentioned in the issue, then inspect how conversation IDs are currently obtained through memory storage. Confirm which ChatMemory implementations and tests are affected; done means the interface exposes conversation IDs without requiring repository injection and the behavior is covered by tests.