Cross-Platform Crucible (#2)

Crucible groundwork for cross-platform compatibility.

Reviewed-on: #2
Reviewed-by: xtul <mpiasecki720@protonmail.com>
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

internal/music/music_test.go

@@ -402,3 +402,16 @@ func TestResolveFFprobeEnv(t *testing.T) {
 		t.Fatalf("expected '/custom/ffprobe', got %q", path)
 	}
 }
+
+func TestFFmpegMissingErrHasInstallHints(t *testing.T) {
+	msg := ffmpegMissingErr("ffmpeg").Error()
+	for _, want := range []string{"ffmpeg", "winget", "brew", "apt", "SOW_FFMPEG"} {
+		if !strings.Contains(msg, want) {
+			t.Errorf("ffmpeg error missing %q; got:\n%s", want, msg)
+		}
+	}
+	probe := ffmpegMissingErr("ffprobe").Error()
+	if !strings.Contains(probe, "SOW_FFPROBE") {
+		t.Errorf("ffprobe error should mention SOW_FFPROBE; got:\n%s", probe)
+	}
+}