Gate READY on download completion; move audio to ~/.radiantwave/audio

State machine now uses DOWNLOADING_ASSETS before READY. Downloads closing
the DownloadDone channel signals checkState() to proceed. Download failure
sets downloadFailed flag which prevents READY. Audio files moved from
~/.local/share/rhemawave/audio to ~/.radiantwave/audio/.

Regression tests in application_test.go (linux build-tagged due to
network package D-Bus init). Version 0.6.

internal/page/home.go

@@ -13,7 +13,7 @@ import (
 	"rhemawavetech.com/rhemawave/internal/shaderManager"
 )
 
-var GitVersion = "Audio-Bug-Fix 0.5"
+var GitVersion = "Audio-Bug-Fix 0.6"
 
 type Home struct {
 	Base
@@ -31,6 +31,7 @@ type Home struct {
 	hasLicenseInfo       bool
 	baseFontSize         int
 	isDownloadComplete   bool
+	downloadFailed       bool
 }
 
 // Init performs basic page initialization and creation of static assets.
@@ -172,8 +173,13 @@ func (p *Home) Update(dt float32) error {
 		case progressUpdate, ok = <-p.Context.MessageChannel:
 			gotUpdate = true
 			if !ok {
-				p.setMessage("Status: READY", colors.Green)
-				p.isDownloadComplete = true
+				if p.downloadFailed {
+					p.setMessage("Download failed — restart to retry", colors.Red)
+				} else {
+					p.setMessage("Status: READY", colors.Green)
+					p.isDownloadComplete = true
+					close(p.Context.DownloadDone)
+				}
 				return nil
 			}
 		default:
@@ -187,6 +193,7 @@ drained:
 	}
 
 	if progressUpdate.Err != nil {
+		p.downloadFailed = true
 		p.setMessage(fmt.Sprintf("Error: %s", progressUpdate.Err.Error()), colors.Red)
 		return nil
 	}