More reliable live tempo and key feedback

Improve live tempo and key detection

The Studio Analyzer now shows clearer automatic beat tracking feedback, discards stale evidence on reacquisition and source changes, and avoids presenting an unverified tempo as a lock. Live key detection now follows longer harmonic history, handles uncertain or noisy input more cautiously, and resets its evidence when input changes. Tempo and key estimates remain musical interpretations that may be ambiguous.