Refactor plotting logic into separate package and update .gitignore

- Move PlotIR function from pkg/convolve to pkg/plot package
- Update main.go to use new plot package
- Clean up convolve package imports
- Add comprehensive .gitignore entries for test files and generated outputs
- Allow only recorded.wav and sweep.wav in testfiles directory
- Ignore all generated audio files and plot images

.gitignore

@@ -41,4 +41,25 @@ ehthumbs.db
 .dagger/
 
 # Environment files
-.env 
+.env
+
+# Test files - ignore all except recorded.wav and sweep.wav
+testfiles/*
+!testfiles/recorded.wav
+!testfiles/sweep.wav
+
+# Generated IR files and plots
+*.wav
+*.flac
+*.png
+*.jpg
+*.jpeg
+*.tiff
+*.tif
+*.pdf
+*.svg
+*.eps
+
+# But allow the specific test files
+!testfiles/recorded.wav
+!testfiles/sweep.wav