A failed upstream call returned HTTP 200 with a hash-derived answer that the UI
rendered with the same P(FAVORABLE) and CONFIDENCE figures as a real decision.
The fallback is now badged OFFLINE with those derived numbers blanked out.
Request errors also rendered "SIGNS POINT TO YES" and always reported a network
timeout. Failures now show CANNOT PREDICT and the real HTTP status or backend
message, and the stored history is validated before use so a malformed value
cannot break the whole interface.
