harden deezer quality fallback and metadata handling

Improve Deezer full-quality mode behavior by returning explicit errors when yt-dlp mode fails with fallback disabled, parse structured API errors, and correctly map explicit_lyrics booleans into explicit tags.

internal/provider/deezer/client.go

@@ -175,7 +175,7 @@ func (c *Client) GetDownloadable(ctx context.Context, item string, _ int) (*prov
 			return d, nil
 		}
 		if !c.cfg.Session.Deezer.LowerQualityIfNotAvailable {
-			return nil, dlErr
+			return nil, fmt.Errorf("deezer full-quality mode failed and fallback is disabled: %w", dlErr)
 		}
 	}
 	preview := strings.TrimSpace(stringFromAny(meta["preview"]))
@@ -352,8 +352,15 @@ func (c *Client) apiGet(ctx context.Context, path string, params url.Values) (ma
 	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 		return nil, fmt.Errorf("deezer api failed: status=%d body=%s", resp.StatusCode, string(body))
 	}
-	if e := stringFromAny(out["error"]); e != "" {
-		return nil, fmt.Errorf("deezer api error: %s", e)
+	if errObj, ok := out["error"].(map[string]any); ok {
+		msg := strings.TrimSpace(stringFromAny(errObj["message"]))
+		if msg == "" {
+			msg = strings.TrimSpace(stringFromAny(errObj["type"]))
+		}
+		if msg == "" {
+			msg = "unknown deezer error"
+		}
+		return nil, fmt.Errorf("deezer api error: %s", msg)
 	}
 	return out, nil
 }
@@ -375,7 +382,7 @@ func enrichTrack(track map[string]any) {
 			track["media_number"] = d
 		}
 	}
-	if v := stringFromAny(track["explicit_lyrics"]); v == "true" {
+	if boolFromAny(track["explicit_lyrics"]) {
 		track["explicit"] = true
 	}
 }
@@ -441,6 +448,11 @@ func intFromAny(v any) int {
 	}
 }
 
+func boolFromAny(v any) bool {
+	b, ok := v.(bool)
+	return ok && b
+}
+
 func runCommand(ctx context.Context, name string, args ...string) ([]byte, error) {
 	cmd := exec.CommandContext(ctx, name, args...)
 	b, err := cmd.CombinedOutput()