feat: 引入 Eino 框架并实现 AI 编排层基础设施与节点

- 引入 cloudwego/eino v0.9.9 和 eino-ext/components/model/openai v0.1.13
- 新增 internal/eino/ 包：
  - types.go: PipelineInput/Output、STTOutput、TokenUsage 类型定义
  - state.go: PipelineState 跨节点状态收集（线程安全）
  - callback.go: ChatModel OnEndWithStreamOutput 回调，逐 token 推送 llm_chunk
  - nodes_stt.go: STT Lambda，支持文本/语音输入模式
  - nodes_history.go: 历史组装 Lambda，含多模态图片支持
  - nodes_splitter.go: 句子分割 Transform Lambda
  - nodes_tts.go: TTS Lambda，逐句合成推送音频
  - nodes_done.go: Done Lambda，发送 llm_done 并追加历史

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

backend/go.mod

@@ -13,16 +13,24 @@ require (
 	github.com/spf13/viper v1.21.0
 	github.com/stretchr/testify v1.11.1
 	go.uber.org/zap v1.28.0
-	golang.org/x/crypto v0.23.0
+	golang.org/x/crypto v0.31.0
 )
 
 require (
-	github.com/bytedance/sonic v1.11.6 // indirect
-	github.com/bytedance/sonic/loader v0.1.1 // indirect
+	github.com/bahlo/generic-list-go v0.2.0 // indirect
+	github.com/buger/jsonparser v1.1.1 // indirect
+	github.com/bytedance/gopkg v0.1.3 // indirect
+	github.com/bytedance/sonic v1.15.0 // indirect
+	github.com/bytedance/sonic/loader v0.5.0 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
-	github.com/cloudwego/base64x v0.1.4 // indirect
-	github.com/cloudwego/iasm v0.2.0 // indirect
+	github.com/cloudwego/base64x v0.1.6 // indirect
+	github.com/cloudwego/eino v0.9.9 // indirect
+	github.com/cloudwego/eino-ext/components/model/openai v0.1.13 // indirect
+	github.com/cloudwego/eino-ext/libs/acl/openai v0.1.17 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/eino-contrib/jsonschema v1.0.3 // indirect
+	github.com/evanphx/json-patch v0.5.2 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/gabriel-vasile/mimetype v1.4.3 // indirect
 	github.com/gin-contrib/sse v0.1.0 // indirect
@@ -31,18 +39,25 @@ require (
 	github.com/go-playground/validator/v10 v10.20.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
 	github.com/goccy/go-json v0.10.2 // indirect
+	github.com/goph/emperror v0.17.2 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.10 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
+	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/meguminnnnnnnnn/go-openai v0.1.2 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/nikolalohinski/gonja v1.5.3 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/sagikazarmark/locafero v0.11.0 // indirect
+	github.com/sirupsen/logrus v1.9.3 // indirect
+	github.com/slongfield/pyfmt v0.0.0-20220222012616-ea85ff4c361f // indirect
 	github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8 // indirect
 	github.com/spf13/afero v1.15.0 // indirect
 	github.com/spf13/cast v1.10.0 // indirect
@@ -51,10 +66,13 @@ require (
 	github.com/subosito/gotenv v1.6.0 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.12 // indirect
+	github.com/wk8/go-ordered-map/v2 v2.1.8 // indirect
+	github.com/yargevad/filepathx v1.0.0 // indirect
 	go.uber.org/atomic v1.11.0 // indirect
 	go.uber.org/multierr v1.10.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
-	golang.org/x/arch v0.8.0 // indirect
+	golang.org/x/arch v0.11.0 // indirect
+	golang.org/x/exp v0.0.0-20230713183714-613f0c0eb8a1 // indirect
 	golang.org/x/net v0.25.0 // indirect
 	golang.org/x/sync v0.17.0 // indirect
 	golang.org/x/sys v0.30.0 // indirect