feat: reimplement WAV extraction in Go (replaces extract_wavs.sh)

extract.go replaces the bash script with idiomatic Go:
- akaiutil process communication via stdin/stdout pipes
- partition enumeration (df output parsing)
- volume enumeration (dir output parsing per partition)
- sample2wavall per volume with WAV count aggregation

runAkaiutil is a package-level var — tests stub it with canned
output to verify parsing without a real akaiutil binary or ISO.

Removed: findScript(), -tool flag on extract, os/exec from main.go
Kept: extract_wavs.sh as a standalone utility (no longer called)

main.go

@@ -8,7 +8,6 @@ import (
 	"net/http"
 	"net/url"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"sort"
 	"strconv"
@@ -100,10 +99,9 @@ Download flags:
   -dir "./isos"            output directory (default: current dir)
   -jobs 2                  concurrent downloads (default: 2)
 
-Extract flags:
+	Extract flags:
   -dir "./isos"            directory containing ISO files
   -out "./wavs"            output directory for WAV files
-  -tool "./extract_wavs.sh" path to extraction script
   -jobs 2                  concurrent extractions (default: 2)
 
 Pipeline flags:
@@ -382,15 +380,9 @@ func cmdExtract(args []string) {
 	fs := flag.NewFlagSet("extract", flag.ExitOnError)
 	isoDir := fs.String("dir", ".", "directory with ISO files")
 	outDir := fs.String("out", "./wavs", "output directory for WAVs")
-	toolFlag := fs.String("tool", "", "path to extraction script (default: auto-detect)")
 	jobs := fs.Int("jobs", 2, "concurrent extractions")
 	_ = fs.Parse(args)
 
-	toolPath := *toolFlag
-	if toolPath == "" {
-		toolPath = findScript("extract_wavs.sh")
-	}
-
 	os.MkdirAll(*outDir, 0755)
 
 	entries, err := os.ReadDir(*isoDir)
@@ -414,8 +406,6 @@ func cmdExtract(args []string) {
 
 	sem := make(chan struct{}, *jobs)
 	var wg sync.WaitGroup
-	var mu sync.Mutex
-	results := map[string]string{}
 
 	for _, iso := range isos {
 		wg.Add(1)
@@ -425,10 +415,7 @@ func cmdExtract(args []string) {
 			defer func() { <-sem }()
 
 			out := *outDir
-			result, err := extractISO(toolPath, isoPath, out)
-			mu.Lock()
-			results[filepath.Base(isoPath)] = result
-			mu.Unlock()
+			result, err := extractISO(isoPath, out)
 			if err != nil {
 				fmt.Printf("  FAIL  %-40s  %v\n", filepath.Base(isoPath), err)
 			} else {
@@ -439,46 +426,6 @@ func cmdExtract(args []string) {
 	wg.Wait()
 }
 
-func extractISO(toolPath, isoPath, outDir string) (string, error) {
-	absTool, err := filepath.Abs(toolPath)
-	if err != nil {
-		return "", err
-	}
-	if _, err := os.Stat(absTool); os.IsNotExist(err) {
-		return "", fmt.Errorf("script not found: %s", absTool)
-	}
-
-	isoOutDir := filepath.Join(outDir, sanitiseISOName(filepath.Base(isoPath)))
-
-	if _, err := os.Stat(isoOutDir); err == nil {
-		var wavCount int
-		filepath.WalkDir(isoOutDir, func(p string, d os.DirEntry, err error) error {
-			if err == nil && !d.IsDir() && strings.HasSuffix(strings.ToLower(d.Name()), ".wav") {
-				wavCount++
-			}
-			return nil
-		})
-		if wavCount > 0 {
-			return fmt.Sprintf("skipped (%d WAVs exist)", wavCount), nil
-		}
-	}
-
-	cmd := exec.Command("bash", absTool, isoPath, outDir)
-	cmd.Stderr = nil
-	output, err := cmd.Output()
-	if err != nil {
-		return "", fmt.Errorf("extract: %w", err)
-	}
-
-	lines := strings.Split(string(output), "\n")
-	for _, line := range lines {
-		if strings.Contains(line, "Total WAV files:") {
-			return strings.TrimSpace(line), nil
-		}
-	}
-	return "extracted (check output)", nil
-}
-
 func sanitiseISOName(path string) string {
 	name := path
 	if ext := filepath.Ext(name); ext != "" {
@@ -520,7 +467,6 @@ func cmdPipeline(args []string) {
 
 	isoDir := filepath.Join(*baseDir, "isos")
 	wavDir := filepath.Join(*baseDir, "wavs")
-	toolPath := findScript("extract_wavs.sh")
 
 	// Remaining args after flags are treated as explicit identifiers
 	identifiers := fs.Args()
@@ -566,28 +512,13 @@ func cmdPipeline(args []string) {
 	cmdDownload([]string{"-f", idFile, "-dir", isoDir, "-jobs", fmt.Sprintf("%d", *dlJobs)})
 
 	fmt.Println("\n=== Phase 3: Extract ===")
-	cmdExtract([]string{"-dir", isoDir, "-out", wavDir, "-tool", toolPath, "-jobs", fmt.Sprintf("%d", *extJobs)})
+	cmdExtract([]string{"-dir", isoDir, "-out", wavDir, "-jobs", fmt.Sprintf("%d", *extJobs)})
 
 	fmt.Printf("\n=== Pipeline Complete ===\n")
 	fmt.Printf("  ISOs: %s\n", isoDir)
 	fmt.Printf("  WAVs: %s\n", wavDir)
 }
 
-func findScript(name string) string {
-	candidates := []string{
-		filepath.Join(filepath.Dir(os.Args[0]), name),
-		filepath.Join(filepath.Dir(os.Args[0]), "scripts", name),
-		name,
-		filepath.Join("scripts", name),
-	}
-	for _, p := range candidates {
-		if _, err := os.Stat(p); err == nil {
-			return p
-		}
-	}
-	return name
-}
-
 // ─── Helpers ───────────────────────────────────────────────────────────
 
 func fatal(format string, args ...any) {