Selection analysis responsiveness update.
- Moved selection frequency analysis to a cancellable background Worker so long selections no longer block the Webview UI.
- Kept dominant frequency, spectral centroid, and band percentages exact over the full selected range.
- Added a blue calculating state for delayed frequency metrics while keeping time-domain metrics visible immediately.
- Made selection WAV export request the save path before encoding and encode large exports in chunks, so downloading a selection does not block delayed selection analysis results.
- Added an opt-in spectrogram profiling setting for local performance diagnostics.
- Reduced extension activation overhead while preserving audio-path actions in opened text/code files.