i18n: 中文化所有错误消息和用户交互文本

- Go 后端 handler 错误消息统一中文化（middleware/repos/generate/review/settings）
- 前端 JS 加载和错误消息中文化（diff-viewer.js, graph.js）
- 模板页面错误 fallback 和静态文本中文化（index/generate/review/base）
- 消除中英文混杂，提升中文用户体验

handlers/generate.go

@@ -22,7 +22,7 @@ func NewGenerateHandler(db *sql.DB) *GenerateHandler {
 func (h *GenerateHandler) Generate(c *gin.Context) {
 	user := GetCurrentUser(c)
 	if user == nil {
-		c.JSON(http.StatusUnauthorized, gin.H{"error": "unauthenticated"})
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "未登录"})
 		return
 	}
 
@@ -32,7 +32,7 @@ func (h *GenerateHandler) Generate(c *gin.Context) {
 	var localPath string
 	err := h.db.QueryRow(`SELECT local_path FROM repositories WHERE id = ? AND user_id = ?`, id, user.ID).Scan(&localPath)
 	if err == sql.ErrNoRows {
-		c.JSON(http.StatusNotFound, gin.H{"error": "repository not found"})
+		c.JSON(http.StatusNotFound, gin.H{"error": "仓库未找到"})
 		return
 	}
 	if err != nil {
@@ -46,7 +46,7 @@ func (h *GenerateHandler) Generate(c *gin.Context) {
 		Head string `json:"head" binding:"required"`
 	}
 	if err := c.ShouldBindJSON(&req); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "base and head are required"})
+		c.JSON(http.StatusBadRequest, gin.H{"error": "请选择 Base 和 Head 分支"})
 		return
 	}
 
@@ -59,14 +59,14 @@ func (h *GenerateHandler) Generate(c *gin.Context) {
 
 	flusher, ok := c.Writer.(http.Flusher)
 	if !ok {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": "streaming not supported"})
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "服务器不支持流式传输"})
 		return
 	}
 
 	sendEvent := func(event string, data interface{}) {
 		jsonData, err := json.Marshal(data)
 		if err != nil {
-			jsonData = []byte(`{"error":"failed to marshal event data"}`)
+			jsonData = []byte(`{"error":"序列化事件数据失败"}`)
 		}
 		fmt.Fprintf(c.Writer, "event: %s\ndata: %s\n\n", event, jsonData)
 		flusher.Flush()
@@ -85,12 +85,12 @@ func (h *GenerateHandler) Generate(c *gin.Context) {
 	// Save analysis to DB with user_id
 	resultJSON, err := json.Marshal(pr)
 	if err != nil {
-		sendEvent("error", map[string]interface{}{"message": "marshal result: " + err.Error()})
+		sendEvent("error", map[string]interface{}{"message": "序列化结果失败: " + err.Error()})
 		return
 	}
 	if _, err := h.db.Exec(`INSERT INTO analyses (user_id, repo_id, type, base_ref, head_ref, result) VALUES (?, ?, 'pr_description', ?, ?, ?)`,
 		user.ID, id, req.Base, req.Head, string(resultJSON)); err != nil {
-		sendEvent("error", map[string]interface{}{"message": "save analysis: " + err.Error()})
+		sendEvent("error", map[string]interface{}{"message": "保存分析结果失败: " + err.Error()})
 		return
 	}
 }