feat(config): 重构配置层为 Viper + YAML + .env 三级加载

- config 改用 Viper 读取 YAML + 绑定环境变量 + godotenv 加载 .env
- 新增 LLM / ImageGen / JWT / Database / Server 分组配置结构
- 新增 backend/.env.example 环境变量模板
- .gitignore 添加 backend/.env 和 backend/main

backend/go.sum

@@ -25,7 +25,11 @@ github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkp
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@@ -43,6 +47,8 @@ github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJn
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@@ -65,6 +71,8 @@ github.com/jinzhu/inflection v1.0.0 h1:K317FqzuhWc8YvSVlFMCCUb36O/S9MCKRDI7QkRKD
 github.com/jinzhu/inflection v1.0.0/go.mod h1:h+uFLlag+Qp1Va5pdKtLDYj+kHp5pxUVkryuEj+Srlc=
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@@ -117,6 +125,8 @@ github.com/quic-go/quic-go v0.59.0/go.mod h1:upnsH4Ju1YkqpLXC305eW3yDZ4NfnNbmQRC
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@@ -126,6 +136,16 @@ github.com/smarty/assertions v1.15.0 h1:cR//PqUBUiQRakZWqBiFFQ9wb8emQGDb0HeGdqGB
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+github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
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@@ -140,6 +160,8 @@ github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXl
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@@ -154,6 +176,8 @@ go.mongodb.org/mongo-driver/v2 v2.5.0 h1:yXUhImUjjAInNcpTcAlPHiT7bIXhshCTL3jVBkF
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+go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
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