feat: implement RAG-based chatbot service with usage limits and history persistence

internal/dtos/request/chatbot.go

@@ -2,7 +2,7 @@ package request
 
 type ChatbotDto struct {
 	ProjectID *string `json:"project_id"`
-	Question  string  `json:"question" validate:"required"`
+	Question  string  `json:"question" validate:"required,max=500"`
 }
 
 type GetChatbotHistoryDto struct {

internal/services/chatbotService.go

@@ -86,8 +86,7 @@ User Question:
 Rules:
 - Reply in the same language as the user's question.
 - If the user is greeting, respond with a friendly greeting and briefly introduce yourself.
-- If the user asks a history-related question, respond exactly:
-<answer>I don't have enough historical context to answer that.</answer>
+- If the user asks a history-related question, respond in the same language as the user's question, stating that you don't have enough historical context to answer that (for example, in Vietnamese: "Tôi không có đủ dữ liệu lịch sử để trả lời câu hỏi này.").
 - Do not answer historical questions from memory.
 - Do not use your own knowledge, assumptions, memory, or external facts.
 - Do not guess, infer, assume, or invent missing information.
@@ -110,8 +109,7 @@ Rules:
 - Never infer information that is not explicitly stated in Context.
 - Never create names, dates, places, events, causes, results, or explanations that are not in Context.
 - Every factual sentence must be directly supported by Context.
-- If Context does not contain enough information to answer, respond exactly:
-<answer>I don't have enough historical context to answer that.</answer>
+- If Context does not contain enough information to answer, respond in the same language as the user's question, stating that you don't have enough historical context to answer that (for example, in Vietnamese: "Tôi không có đủ dữ liệu lịch sử để trả lời câu hỏi này.").
 - If Context only partially answers the question, answer only the supported part and clearly say the remaining information is not available in the provided context.
 - Do not mention document scores.
 - Do not cite documents unless the user asks.

pkg/constants/usage.go

@@ -3,6 +3,6 @@ package constants
 import "time"
 
 const (
-	MaxDailyAIUsage = 1000
+	MaxDailyAIUsage = 50
 	UsageExpiration = 24 * time.Hour
 )