feat: 添加本地缓存功能，减少API调用

- 实现SQLite缓存模块，支持高效查询和存储
- 添加缓存键生成策略（基于原文+语言对的SHA256哈希）
- 集成缓存到Translator类，先查缓存再调用API
- 添加缓存管理命令：cache clear, cache stats, cache cleanup
- 实现组合缓存清理策略（数量限制+时间过期）
- 添加完整的单元测试
- 更新配置文件模板，添加缓存配置
- 更新文档和版本记录

版本: v0.5.1

internal/translator/translator.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/titor/fanyi/internal/cache"
 	"github.com/titor/fanyi/internal/config"
 	"github.com/titor/fanyi/internal/content"
 	"github.com/titor/fanyi/internal/provider"
@@ -16,16 +17,32 @@ type Translator struct {
 	provider      provider.Provider
 	prompt        *PromptManager
 	contentParser *content.Parser
+	cache         cache.Cache
 }
 
 // NewTranslator 创建翻译器实例
 func NewTranslator(config *config.Config, provider provider.Provider) *Translator {
-	return &Translator{
+	translator := &Translator{
 		config:        config,
 		provider:      provider,
 		prompt:        NewPromptManager(config.Prompts),
 		contentParser: content.NewParser(config.SkipKeywords),
 	}
+
+	// 初始化缓存（如果启用）
+	if config.Cache.Enabled {
+		cacheConfig := &cache.CacheConfig{
+			Enabled:    config.Cache.Enabled,
+			MaxRecords: config.Cache.MaxRecords,
+			ExpireDays: config.Cache.ExpireDays,
+			DBPath:     config.Cache.DBPath,
+		}
+		if cacheInstance, err := cache.NewSQLiteCache(cacheConfig); err == nil {
+			translator.cache = cacheInstance
+		}
+	}
+
+	return translator
 }
 
 // Translate 执行翻译
@@ -68,6 +85,26 @@ func (t *Translator) Translate(ctx context.Context, text string, options *Transl
 		Options:  options.ExtraOptions,
 	}
 
+	// 检查缓存
+	if t.cache != nil {
+		cacheKey := cache.GenerateCacheKey(filteredText, options.FromLang, options.ToLang)
+		if cachedEntry, err := t.cache.Get(ctx, cacheKey); err == nil && cachedEntry != nil {
+			// 缓存命中
+			return &TranslateResult{
+				Original:   text,
+				Translated: cachedEntry.TranslatedText,
+				FromLang:   cachedEntry.FromLang,
+				ToLang:     cachedEntry.ToLang,
+				Model:      cachedEntry.Model,
+				Usage: &provider.Usage{
+					PromptTokens:     cachedEntry.PromptTokens,
+					CompletionTokens: cachedEntry.CompletionTokens,
+					TotalTokens:      cachedEntry.TotalTokens,
+				},
+			}, nil
+		}
+	}
+
 	// 调用厂商API
 	resp, err := t.provider.Translate(timeoutCtx, req)
 	if err != nil {
@@ -81,6 +118,26 @@ func (t *Translator) Translate(ctx context.Context, text string, options *Transl
 		translatedText = t.contentParser.Reconstruct(parseResult, resp.Text)
 	}
 
+	// 保存到缓存
+	if t.cache != nil {
+		cacheKey := cache.GenerateCacheKey(filteredText, options.FromLang, options.ToLang)
+		cacheEntry := &cache.CacheEntry{
+			CacheKey:         cacheKey,
+			OriginalText:     filteredText,
+			TranslatedText:   translatedText,
+			FromLang:         resp.FromLang,
+			ToLang:           resp.ToLang,
+			Model:            resp.Model,
+			PromptName:       options.PromptName,
+			PromptContent:    prompt,
+			PromptTokens:     resp.Usage.PromptTokens,
+			CompletionTokens: resp.Usage.CompletionTokens,
+			TotalTokens:      resp.Usage.TotalTokens,
+		}
+		// 异步保存缓存，不阻塞翻译结果返回
+		go t.cache.Set(context.Background(), cacheEntry)
+	}
+
 	// 构建结果
 	return &TranslateResult{
 		Original:   text,