refactor: 使用 go-sora2api SDK 替代自建 Sora 客户端

使用 go-sora2api v1.1.0 SDK 替代原有 ~2000 行自建 HTTP/PoW/TLS 指纹代码，
SDK 提供高并发性能优化（实例级 rand、PoW 缓冲区复用、context.Context 支持）。

- 新增 SoraSDKClient 适配器实现 SoraClient 接口
- 精简 sora_client.go 为仅保留接口和类型定义
- 更新 Wire 绑定使用 SoraSDKClient
- 删除 SoraDirectClient、sora_curl_cffi_sidecar、sora_request_guard 等旧代码

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/go.mod

@@ -5,6 +5,7 @@ go 1.25.7
 require (
 	entgo.io/ent v0.14.5
 	github.com/DATA-DOG/go-sqlmock v1.5.2
+	github.com/DouDOU-start/go-sora2api v1.1.0
 	github.com/alitto/pond/v2 v2.6.2
 	github.com/cespare/xxhash/v2 v2.3.0
 	github.com/dgraph-io/ristretto v0.2.0
@@ -29,10 +30,10 @@ require (
 	github.com/tidwall/sjson v1.2.5
 	github.com/zeromicro/go-zero v1.9.4
 	go.uber.org/zap v1.24.0
-	golang.org/x/crypto v0.47.0
+	golang.org/x/crypto v0.48.0
 	golang.org/x/net v0.49.0
 	golang.org/x/sync v0.19.0
-	golang.org/x/term v0.39.0
+	golang.org/x/term v0.40.0
 	gopkg.in/natefinch/lumberjack.v2 v2.2.1
 	gopkg.in/yaml.v3 v3.0.1
 	modernc.org/sqlite v1.44.3
@@ -46,7 +47,14 @@ require (
 	github.com/agext/levenshtein v1.2.3 // indirect
 	github.com/andybalholm/brotli v1.2.0 // indirect
 	github.com/apparentlymart/go-textseg/v15 v15.0.0 // indirect
+	github.com/bdandy/go-errors v1.2.2 // indirect
+	github.com/bdandy/go-socks4 v1.2.3 // indirect
 	github.com/bmatcuk/doublestar v1.3.4 // indirect
+	github.com/bogdanfinn/fhttp v0.6.8 // indirect
+	github.com/bogdanfinn/quic-go-utls v1.0.9-utls // indirect
+	github.com/bogdanfinn/tls-client v1.14.0 // indirect
+	github.com/bogdanfinn/utls v1.7.7-barnius // indirect
+	github.com/bogdanfinn/websocket v1.5.5-barnius // indirect
 	github.com/boombuler/barcode v1.0.1-0.20190219062509-6c824513bacc // indirect
 	github.com/bytedance/sonic v1.9.1 // indirect
 	github.com/cenkalti/backoff/v4 v4.3.0 // indirect
@@ -123,6 +131,7 @@ require (
 	github.com/spf13/cast v1.6.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
+	github.com/tam7t/hpkp v0.0.0-20160821193359-2b70b4024ed5 // indirect
 	github.com/testcontainers/testcontainers-go v0.40.0 // indirect
 	github.com/tidwall/match v1.1.1 // indirect
 	github.com/tidwall/pretty v1.2.0 // indirect
@@ -144,9 +153,9 @@ require (
 	go.uber.org/multierr v1.9.0 // indirect
 	golang.org/x/arch v0.3.0 // indirect
 	golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
-	golang.org/x/mod v0.31.0 // indirect
-	golang.org/x/sys v0.40.0 // indirect
-	golang.org/x/text v0.33.0 // indirect
+	golang.org/x/mod v0.32.0 // indirect
+	golang.org/x/sys v0.41.0 // indirect
+	golang.org/x/text v0.34.0 // indirect
 	google.golang.org/grpc v1.75.1 // indirect
 	google.golang.org/protobuf v1.36.10 // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect