feat(web): integrate custom providers into the provider credentials section

- Merge the separate custom-providers section into the unified provider
  grid; "Custom" in the add-provider picker now acts as an add-new action
  (trailing + mark) and opens the dedicated modal, supporting multiple
  OpenAI-compatible endpoints
- Simplify the custom provider modal: drop the default-model field, add
  an inline delete button, align colors with the theme
- Keep the legacy single "custom" card visible (models page, chat
  dropdown and legacy config page) while custom_api_key/custom_api_base
  is still in use, so existing single-provider setups don't disappear
- Unify user-facing wording from "vendor" to "provider" in UI and docs
- Restructure custom provider docs (zh/en/ja) around Web console and
  config file usage

docs/ja/models/custom.mdx

@@ -1,69 +1,31 @@
 ---
-title: Custom
-description: Custom vendor configuration for third-party API proxies and local models
+title: カスタム
+description: サードパーティ API プロキシやローカルモデル向けのカスタムプロバイダー設定
 ---
 
-For model services accessed via the OpenAI-compatible protocol or locally deployed models, such as:
+OpenAI 互換プロトコルで接続するモデルサービス向けの設定です。例えば：
 
-- **Third-party API proxies**: call multiple models through a unified API base
-- **Local models**: models deployed locally with tools like Ollama, vLLM, LocalAI
-- **Private deployments**: model services deployed inside an enterprise
+- **サードパーティ API プロキシ**：統一された API アドレスで複数のモデルを呼び出す
+- **ローカルモデル**：Ollama、vLLM などのツールでローカルにデプロイしたモデル
+- **プライベートデプロイ**：企業内部にデプロイされたモデルサービス
 
-<Note>
-  Difference from the `openai` vendor: when a custom vendor is selected, switching models via `/config model` does not automatically switch the vendor type — the custom API address is always used.
-</Note>
+## Web コンソールでの設定
 
-## Text Chat
+推奨方法です。Web コンソールの「モデル」ページで「プロバイダーを追加」をクリックし、「カスタム」を選択して、名称・API Base・API Key を入力します。複数のカスタムプロバイダーを追加でき、追加後は「メインモデル」でプロバイダーとモデルを選択すると有効になります。
 
-### Third-party API proxy
+<img width="900" src="https://cdn.jsdelivr.net/gh/zhayujie/cowagent-assets@main/screenshots/en/web-console-custom-model-config.png" />
 
-```json
-{
-  "bot_type": "custom",
-  "model": "",
-  "custom_api_key": "YOUR_API_KEY",
-  "custom_api_base": "https://{your-proxy.com}/v1"
-}
-```
+主なローカルデプロイツールのデフォルトアドレス：
 
-| Parameter | Description |
-| --- | --- |
-| `bot_type` | Must be set to `custom` |
-| `model` | Model name; any model name supported by the proxy service |
-| `custom_api_key` | API key provided by the proxy service |
-| `custom_api_base` | API endpoint provided by the proxy service; must be OpenAI-compatible |
-
-### Local models
-
-Local models usually do not require an API key — only the API base needs to be filled in:
-
-```json
-{
-  "bot_type": "custom",
-  "model": "qwen3.5:27b",
-  "custom_api_base": "http://localhost:11434/v1"
-}
-```
-
-Common local deployment tools and their default endpoints:
-
-| Tool | Default API Base |
+| ツール | デフォルト API Base |
 | --- | --- |
 | [Ollama](https://ollama.com) | `http://localhost:11434/v1` |
 | [vLLM](https://docs.vllm.ai) | `http://localhost:8000/v1` |
 | [LocalAI](https://localai.io) | `http://localhost:8080/v1` |
 
-### Switching Models
+## 設定ファイルでの設定
 
-Switching models under a custom vendor only changes `model` — `bot_type` and the API endpoint remain unchanged:
-
-```
-/config model qwen3.5:27b
-```
-
-## Configuring Multiple Custom Providers
-
-If you need to configure several OpenAI-compatible third-party services at once (e.g. SiliconFlow, Qiniu), use the `custom_providers` list and activate one by setting `bot_type` to `"custom:<id>"`:
+`config.json` を直接編集することもできます。`custom_providers` リストに複数のプロバイダーを定義し、`bot_type` を `"custom:<id>"` に設定していずれかを有効化します：
 
 ```json
 {
@@ -71,34 +33,30 @@ If you need to configure several OpenAI-compatible third-party services at once
   "custom_providers": [
     {
       "id": "3f2a9c1b",
-      "name": "siliconflow",
-      "api_key": "YOUR_SILICONFLOW_KEY",
-      "api_base": "https://api.siliconflow.cn/v1",
-      "model": "deepseek-ai/DeepSeek-V3"
+      "name": "プロバイダーA",
+      "api_key": "YOUR_API_KEY_A",
+      "api_base": "https://api.a.com/v1",
+      "model": "deepseek-v3"
     },
     {
       "id": "a1b2c3d4",
-      "name": "qiniu",
-      "api_key": "YOUR_QINIU_KEY",
-      "api_base": "https://api.qnaigc.com/v1",
-      "model": "deepseek-v3"
+      "name": "プロバイダーB",
+      "api_key": "YOUR_API_KEY_B",
+      "api_base": "https://api.b.com/v1",
+      "model": "qwen3-max"
     }
   ]
 }
 ```
 
-| Parameter | Description |
+| パラメータ | 説明 |
 | --- | --- |
-| `custom_providers` | List of custom providers; each item has `id`, `name`, `api_key`, `api_base`, and an optional `model` |
-| `bot_type` | Set to `"custom:<id>"` to activate a specific provider; `id` is the provider's unique identifier |
-| `id` | Server-generated short identifier (8-char hex); used as the primary key for each provider |
-| `name` | User-facing display label — can be freely renamed without breaking anything |
-| `model` | Optional; when set, this model is used instead of the global `model` field |
+| `custom_providers` | カスタムプロバイダーのリスト。各項目は `id`、`name`、`api_base`、`api_key`（任意）、`model`（任意）を含む |
+| `bot_type` | `"custom:<id>"` に設定して対応するプロバイダーを有効化 |
+| `id` | 一意の識別子（8 桁の 16 進数）。Web コンソールから追加すると自動生成され、手動設定の場合は重複しない任意の文字列でよい |
+| `name` | 表示名。自由に変更可能 |
+| `model` | このプロバイダーで使用するモデル。有効化時に適用される |
 
 <Note>
-  The `id` is auto-generated by the web console when you add a provider — you don't need to create it manually. If editing `config.json` by hand, use any unique 8-character hex string (e.g. run `python3 -c "import uuid; print(uuid.uuid4().hex[:8])"`).
-</Note>
-
-<Note>
-  When `bot_type` is exactly `"custom"` (no colon suffix), CowAgent uses the legacy single-provider `custom_api_key` / `custom_api_base` fields, so existing configurations keep working without any changes.
+  従来の単一プロバイダー設定（`bot_type` を `"custom"` にし、`custom_api_key` / `custom_api_base` を使用）は引き続き互換性があり、変更なしでそのまま利用できます。
 </Note>