[Feature] Server-side multi-provider/model support (#583)

* [Feature] Server side multi-pvorider/model support

* copilot suggesition implemented

* feat: improve model selector UI and auto-select default server model

- Replace emoji headers with Lucide icons (Monitor, User)
- Fix transition-all to explicit properties per web guidelines
- Use CSS padding instead of hardcoded space indentation
- Add ModelSelectorSectionHeader component for section headers
- Replace Star icon with "default" text label
- Style Configure button with muted text color
- Auto-select default server model when page loads
- Support AI_MODELS_CONFIG env var for cloud deployments
- Support custom apiKeyEnv/baseUrlEnv per provider config

* docs: update server-side multi-model configuration documentation

- Add AI_MODELS_CONFIG env var option for cloud deployments
- Document apiKeyEnv and baseUrlEnv fields for custom env var names
- Document default field for auto-selecting default model
- Remove deprecated version field from examples
- Add field reference table for clarity

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

lib/i18n/dictionaries/en.json

@@ -305,10 +305,13 @@
         "noModelsFound": "No models found.",
         "default": "Default",
         "serverDefault": "Server Default",
+        "serverModels": "Server Models",
+        "userModels": "User Models",
         "configureModels": "Configure Models...",
         "onlyVerifiedShown": "Only verified models are shown",
         "showUnvalidatedModels": "Show unvalidated models",
         "allModelsShown": "All models are shown (including unvalidated)",
-        "unvalidatedModelWarning": "This model has not been validated"
+        "unvalidatedModelWarning": "This model has not been validated",
+        "serverDefaultModel": "Server default model"
     }
 }

lib/i18n/dictionaries/ja.json

@@ -305,10 +305,13 @@
         "noModelsFound": "モデルが見つかりません。",
         "default": "デフォルト",
         "serverDefault": "サーバーデフォルト",
+        "serverModels": "サーバーモデル",
+        "userModels": "ユーザーモデル",
         "configureModels": "モデルを設定...",
         "onlyVerifiedShown": "検証済みのモデルのみ表示",
         "showUnvalidatedModels": "未検証のモデルを表示",
         "allModelsShown": "すべてのモデルを表示（未検証を含む）",
-        "unvalidatedModelWarning": "このモデルは検証されていません"
+        "unvalidatedModelWarning": "このモデルは検証されていません",
+        "serverDefaultModel": "サーバーデフォルトモデル"
     }
 }

lib/i18n/dictionaries/zh.json

@@ -305,10 +305,13 @@
         "noModelsFound": "未找到模型。",
         "default": "默认",
         "serverDefault": "服务器默认",
+        "serverModels": "服务器模型",
+        "userModels": "用户模型",
         "configureModels": "配置模型...",
         "onlyVerifiedShown": "仅显示已验证的模型",
         "showUnvalidatedModels": "显示未验证的模型",
         "allModelsShown": "显示所有模型（包括未验证的）",
-        "unvalidatedModelWarning": "此模型尚未验证"
+        "unvalidatedModelWarning": "此模型尚未验证",
+        "serverDefaultModel": "服务器默认模型"
     }
 }