fix: prevent HITL confirmation replay

[huynhtrungcip]

Summary:

• Treat a HITL confirmation as already consumed when the original tool call has a response between the confirmation request and the current confirmation response.
• Add processor-level coverage for replayed confirmations.
• Add REST coverage that verifies replaying the same confirmation ID with a changed payload does not re-execute the tool.

Tests:

• go test ./internal/llminternal -run TestRequestConfirmationRequestProcessor -count=1 -v
• go test ./server/adkrest -run TestRESTHITLConfirmationReplayDoesNotReexecuteTool -count=1 -v
• go test ./internal/llminternal ./server/adkrest -count=1
• go test ./...