fix(gemini): bound cancel goroutine to Download lifetime

internal/protocol/gemini/gemini.go

@@ -100,10 +100,18 @@ func (p *Protocol) downloadWithRedirects(ctx context.Context, req *core.Download
 
 	// Close the connection when the context is cancelled so any
 	// blocking Read returns immediately instead of waiting for the
-	// 30-second deadline.
+	// 30-second deadline. The done channel bounds the goroutine to
+	// the lifetime of this call: when Download returns, defer
+	// close(done) lets the goroutine exit even if the parent context
+	// was never cancelled.
+	done := make(chan struct{})
+	defer close(done)
 	go func() {
-		<-ctx.Done()
+		select {
+		case <-ctx.Done():
 			conn.Close()
+		case <-done:
+		}
 	}()
 
 	// Send request: URL + CRLF