refactor: restructure project to standard Go layout

- Reorganize code into cmd/bilidown and internal/ packages
- Rename client/ to web/ for frontend source
- Remove systray dependency for headless web service
- Embed static files into binary using go:embed
- Update import paths to use internal/ prefix
- Update .gitignore with common patterns

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/task/task_test.go

@@ -0,0 +1,39 @@
+package task_test
+
+import (
+	"bufio"
+	"fmt"
+	"os/exec"
+	"testing"
+)
+
+func TestFFMPEG(t *testing.T) {
+	cmd := exec.Command("ffmpeg", "-i", `E:\bilidown\27.video`, "-i", `E:\bilidown\27.audio`, "-c:v", "copy", "-c:a", "copy", "-progress", "pipe:1", `E:\bilidown\27.mp4`)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	scanner := bufio.NewScanner(stdout)
+	for scanner.Scan() {
+		fmt.Println(">>>", scanner.Text())
+	}
+
+	if err := scanner.Err(); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := cmd.Wait(); err != nil {
+		t.Fatal(err)
+	}
+
+	t.Log("done")
+}
+
+func TestNum(t *testing.T) {
+	t.Log(int64(100999) / 1000)
+}