feat(opencode): add extra options editor for SDK configuration

Add key-value pair editor for configuring additional SDK options like
timeout, setCacheKey, etc. Values are automatically parsed to appropriate
types (number, boolean, object) on save.

- Add `extra` field with serde flatten in Rust backend
- Add index signature to OpenCodeProviderOptions type
- Create ExtraOptionKeyInput component with local state pattern
- Place extra options section above models configuration

src/i18n/locales/en.json

@@ -481,7 +481,15 @@
     "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."
+    "providerKeyInvalid": "Invalid format. Use lowercase letters, numbers, and hyphens only.",
+    "extraOptions": "Extra Options",
+    "extraOptionsHint": "Configure extra SDK options like timeout, setCacheKey, etc. Values are auto-parsed to appropriate types (number, boolean, etc.).",
+    "addExtraOption": "Add",
+    "extraOptionKey": "Key",
+    "extraOptionValue": "Value",
+    "extraOptionKeyPlaceholder": "timeout",
+    "extraOptionValuePlaceholder": "600000",
+    "noExtraOptions": "No extra options configured"
   },
   "providerPreset": {
     "label": "Provider Preset",

src/i18n/locales/ja.json

@@ -481,7 +481,15 @@
     "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。"
+    "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。",
+    "extraOptions": "追加オプション",
+    "extraOptionsHint": "timeout、setCacheKey などの SDK オプションを設定。値は自動的に適切な型（数値、真偽値など）に変換されます。",
+    "addExtraOption": "追加",
+    "extraOptionKey": "キー名",
+    "extraOptionValue": "値",
+    "extraOptionKeyPlaceholder": "timeout",
+    "extraOptionValuePlaceholder": "600000",
+    "noExtraOptions": "追加オプションはありません"
   },
   "providerPreset": {
     "label": "プロバイダータイプ",

src/i18n/locales/zh.json

@@ -481,7 +481,15 @@
     "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"
+    "providerKeyInvalid": "标识格式无效，只能使用小写字母、数字和连字符",
+    "extraOptions": "额外选项",
+    "extraOptionsHint": "配置额外的 SDK 选项，如 timeout、setCacheKey 等。值会自动解析类型（数字、布尔值等）。",
+    "addExtraOption": "添加",
+    "extraOptionKey": "键名",
+    "extraOptionValue": "值",
+    "extraOptionKeyPlaceholder": "timeout",
+    "extraOptionValuePlaceholder": "600000",
+    "noExtraOptions": "暂无额外选项"
   },
   "providerPreset": {
     "label": "预设供应商",