feat(opencode): add manual provider key input with duplicate check

- Add Provider Key input field for OpenCode providers (between icon and name)
- User must manually enter a unique key instead of auto-generating from name
- Real-time validation: format check and duplicate detection
- Key is immutable after creation (disabled in edit mode)
- Remove slugify auto-generation logic from mutations
- Add beforeNameSlot prop to BasicFormFields for extensibility
- Add i18n translations for zh/en/ja

src/i18n/locales/en.json

@@ -475,7 +475,13 @@
     "addModel": "Add Model",
     "modelId": "Model ID",
     "modelName": "Display Name",
-    "noModels": "No models configured"
+    "noModels": "No models configured",
+    "providerKey": "Provider Key",
+    "providerKeyPlaceholder": "my-provider",
+    "providerKeyHint": "Unique identifier in config file. Cannot be changed after creation. Use lowercase letters, numbers, and hyphens only.",
+    "providerKeyRequired": "Provider key is required",
+    "providerKeyDuplicate": "This key is already in use",
+    "providerKeyInvalid": "Invalid format. Use lowercase letters, numbers, and hyphens only."
   },
   "providerPreset": {
     "label": "Provider Preset",

src/i18n/locales/ja.json

@@ -475,7 +475,13 @@
     "addModel": "モデルを追加",
     "modelId": "モデル ID",
     "modelName": "表示名",
-    "noModels": "モデルが設定されていません"
+    "noModels": "モデルが設定されていません",
+    "providerKey": "プロバイダーキー",
+    "providerKeyPlaceholder": "my-provider",
+    "providerKeyHint": "設定ファイルの一意の識別子。作成後は変更できません。小文字、数字、ハイフンのみ使用できます。",
+    "providerKeyRequired": "プロバイダーキーを入力してください",
+    "providerKeyDuplicate": "このキーは既に使用されています",
+    "providerKeyInvalid": "無効な形式です。小文字、数字、ハイフンのみ使用できます。"
   },
   "providerPreset": {
     "label": "プロバイダータイプ",

src/i18n/locales/zh.json

@@ -475,7 +475,13 @@
     "addModel": "添加模型",
     "modelId": "模型 ID",
     "modelName": "显示名称",
-    "noModels": "暂无模型配置"
+    "noModels": "暂无模型配置",
+    "providerKey": "供应商标识",
+    "providerKeyPlaceholder": "my-provider",
+    "providerKeyHint": "配置文件中的唯一标识符，创建后无法修改，只能使用小写字母、数字和连字符",
+    "providerKeyRequired": "请填写供应商标识",
+    "providerKeyDuplicate": "此标识已被使用，请更换",
+    "providerKeyInvalid": "标识格式无效，只能使用小写字母、数字和连字符"
   },
   "providerPreset": {
     "label": "预设供应商",