Add integration tests for device sync

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Summary

• Adds a test:integration Rake task running tests under test/integration/ separately from unit tests
• Adds fixtures:generate_click_track to produce a 120 BPM, 2.5-bar click track WAV (with ACID BPM metadata) used by the integration tests
• Adds integration tests for Octatrack and TP-7 sync covering file copy, format conversion, BPM/cue point handling, sample rate conversion, pad-to-bar-boundary, and round-trip cue point sync

Integration tests skip automatically when no device config is found or the device path is not accessible, so they are safe to run in any environment.