refactor: 彻底移除 .env 依赖，配置统一由 config.yaml + 环境变量驱动

backend/go.mod

@@ -27,7 +27,6 @@ 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/joho/godotenv v1.5.1 // 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

backend/go.sum

@@ -44,8 +44,6 @@ github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
 github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
-github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
-github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
 github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnrnM=
 github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
 github.com/klauspost/cpuid/v2 v2.0.9/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=

backend/internal/config/config.go

@@ -5,7 +5,6 @@ import (
 	"os"
 	"strings"
 
-	"github.com/joho/godotenv"
 	"github.com/spf13/viper"
 )
 
@@ -161,12 +160,6 @@ func Load() (*Config, error) {
 		_ = v.MergeInConfig()
 	}
 
-	// 加载 .env 文件（不覆盖已有环境变量）
-	// 按优先级尝试：当前目录、上级目录（兼容从 backend/ 或项目根目录启动）
-	_ = godotenv.Load()
-	_ = godotenv.Load("../.env")
-	_ = godotenv.Load("../../.env") // 兼容从 backend/cmd/server/ 启动
-
 	// 环境变量覆盖
 	v.SetEnvPrefix("CAMTALK")
 	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))