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/bilibili/wbi.go

@@ -0,0 +1,87 @@
+package bilibili
+
+import (
+	"bilidown/internal/util"
+	"database/sql"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var MIXIN_KEY_ENC_TAB = []int{
+	46, 47, 18, 2, 53, 8, 23, 32, 15, 50, 10, 31, 58, 3, 45, 35,
+	27, 43, 5, 49, 33, 9, 42, 19, 29, 28, 14, 39, 12, 38, 41, 13,
+	37, 48, 7, 16, 24, 55, 40, 61, 26, 17, 0, 1, 60, 51, 30, 4,
+	22, 25, 54, 21, 56, 59, 6, 63, 57, 62, 11, 36, 20, 34, 44, 52,
+}
+
+// GetWebKey 获取最新可用的 WbiKey，自动刷新缓存
+func (client *BiliClient) getWbiKey(db *sql.DB) (wbiKey string, err error) {
+	wbiKey, err = getWbiKeyFromDB(db)
+	if err != nil {
+		return "", err
+	}
+	if wbiKey == "" {
+		// 更新数据库中的 WebKey
+		wbiKey, err = client.getWbiKeyRemote()
+		if err != nil {
+			return "", err
+		}
+		if err = saveWbiKey(db, wbiKey); err != nil {
+			return "", err
+		}
+	}
+	return wbiKey, nil
+}
+
+func (client *BiliClient) GetMixinKey(db *sql.DB) (string, error) {
+	wbiKey, err := client.getWbiKey(db)
+	if err != nil {
+		return "", err
+	}
+	var result string
+	for _, index := range MIXIN_KEY_ENC_TAB {
+		result += string(wbiKey[index])
+	}
+	return result[:32], nil
+}
+
+func WbiSign(params map[string]string, mixinKey string) url.Values {
+	values := url.Values{}
+	for key, value := range params {
+		values.Set(key, value)
+	}
+	wts := strconv.FormatInt(time.Now().Unix(), 10)
+	values.Set("wts", wts)
+	encodeStr := strings.ReplaceAll(values.Encode(), "+", "%20") + mixinKey
+	w_rid := util.MD5Hash(encodeStr)
+	values.Set("w_rid", w_rid)
+	return values
+}
+
+// GetWbiKey 从数据库中获取 wbiKey，如果数据库中不存在记录或记录过期，则返回空字符串但不返回错误
+func getWbiKeyFromDB(db *sql.DB) (wbiKey string, err error) {
+	fields, err := util.GetFields(db, "wbi_key", "wbi_key_update_at")
+	if err != nil {
+		return "", err
+	}
+	// 获取上次更新时间的时间戳，单位是秒
+	updateAt, err := strconv.ParseInt(fields["wbi_key_update_at"], 10, 64)
+	if err != nil {
+		return "", nil
+	}
+	// 注意 key_update_at 单位是秒，判断上次刷新时间是否超过 1 天
+	if time.Now().Unix()-updateAt > 24*60*60 {
+		return "", nil
+	}
+	return fields["wbi_key"], nil
+}
+
+// SaveWbiKey 保存 imgKey 和 subKey 到数据库
+func saveWbiKey(db *sql.DB, wbiKey string) error {
+	return util.SaveFields(db, [][2]string{
+		{"wbi_key", wbiKey},
+		{"wbi_key_update_at", strconv.FormatInt(time.Now().Unix(), 10)},
+	})
+}