feat: 新增语音转文字（ASR）功能

- 后端：新增 /api/audio/transcribe 接口，调用 Ollama whisper 进行语音识别
- 前端：新增 AudioTranscribePage.vue 页面，支持 MP3/WAV/M4A/OGG/FLAC 等格式
- 注册路由、工具卡片、智能助手欢迎语更新

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

eai_agentplatform/backend-go/internal/auth/auth.go

@@ -0,0 +1,58 @@
+package auth
+
+import (
+	"errors"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"golang.org/x/crypto/bcrypt"
+)
+
+// HashPassword bcrypt 哈希
+func HashPassword(password string) (string, error) {
+	b, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	if err != nil {
+		return "", err
+	}
+	return string(b), nil
+}
+
+// VerifyPassword 校验密码
+func VerifyPassword(password, hashed string) bool {
+	return bcrypt.CompareHashAndPassword([]byte(hashed), []byte(password)) == nil
+}
+
+// CreateToken 签发 JWT（HS256），payload 对齐 Python：sub/role/iat/exp
+func CreateToken(username, role, secret string, expireMin int) (string, error) {
+	now := time.Now()
+	claims := jwt.MapClaims{
+		"sub":  username,
+		"role": role,
+		"iat":  now.Unix(),
+		"exp":  now.Add(time.Duration(expireMin) * time.Minute).Unix(),
+	}
+	return jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString([]byte(secret))
+}
+
+// SignClaims 通用 JWT 签发（考试会话等复用）
+func SignClaims(claims jwt.MapClaims, secret string) (string, error) {
+	return jwt.NewWithClaims(jwt.SigningMethodHS256, claims).SignedString([]byte(secret))
+}
+
+// ParseToken 校验 JWT，返回 claims。失败返回 error。
+func ParseToken(tokenStr, secret string) (jwt.MapClaims, error) {
+	token, err := jwt.Parse(tokenStr, func(t *jwt.Token) (any, error) {
+		if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
+			return nil, jwt.ErrSignatureInvalid
+		}
+		return []byte(secret), nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	claims, ok := token.Claims.(jwt.MapClaims)
+	if !ok || !token.Valid {
+		return nil, errors.New("invalid token claims")
+	}
+	return claims, nil
+}