feat: replace text inputs with dropdown selects for OpenClaw agent model config

- Add useOpenClawModelOptions hook to aggregate models from all configured OpenClaw providers
- Replace read-only primary model display with a searchable Select dropdown
- Replace comma-separated fallback text input with add/remove Select rows
- Filter out already-selected models from fallback options
- Show "(not configured)" marker for values whose provider has been deleted
- Unify terminology: rename "主模型/Primary Model" to "默认模型/Default Model"

src/i18n/locales/en.json

@@ -1292,11 +1292,14 @@
       "title": "Agents Config",
       "description": "Manage agents.defaults in openclaw.json (default model, runtime parameters, etc.)",
       "modelSection": "Model Configuration",
-      "primaryModel": "Primary Model",
-      "primaryModelHint": "Set via the \"Set as Default Model\" button in the provider list",
+      "primaryModel": "Default Model",
+      "primaryModelHint": "Select from models of configured providers",
       "notSet": "Not set",
       "fallbackModels": "Fallback Models",
-      "fallbackModelsHint": "Comma-separated, ordered by priority",
+      "fallbackModelsHint": "When the primary model is unavailable, fallbacks are tried in order",
+      "addFallback": "Add fallback model",
+      "noModels": "No configured provider models. Please add an OpenClaw provider first.",
+      "notInList": "{{value}} (not configured)",
       "runtimeSection": "Runtime Parameters",
       "workspace": "Workspace Path",
       "timeout": "Timeout (seconds)",

src/i18n/locales/ja.json

@@ -1292,11 +1292,14 @@
       "title": "Agents 設定",
       "description": "openclaw.json の agents.defaults 設定を管理（デフォルトモデル、ランタイムパラメータなど）",
       "modelSection": "モデル設定",
-      "primaryModel": "プライマリモデル",
-      "primaryModelHint": "プロバイダ一覧の「デフォルトモデルに設定」ボタンで設定します",
+      "primaryModel": "デフォルトモデル",
+      "primaryModelHint": "設定済みプロバイダのモデルから選択してください",
       "notSet": "未設定",
       "fallbackModels": "フォールバックモデル",
-      "fallbackModelsHint": "カンマ区切り、優先度順",
+      "fallbackModelsHint": "プライマリモデルが利用不可の場合、優先度順にフォールバックが試行されます",
+      "addFallback": "フォールバックモデルを追加",
+      "noModels": "設定済みのプロバイダモデルがありません。先に OpenClaw プロバイダを追加してください。",
+      "notInList": "{{value}} (未設定)",
       "runtimeSection": "ランタイムパラメータ",
       "workspace": "ワークスペースパス",
       "timeout": "タイムアウト（秒）",

src/i18n/locales/zh.json

@@ -1292,11 +1292,14 @@
       "title": "Agents 配置",
       "description": "管理 openclaw.json 中的 agents.defaults 配置（默认模型、运行参数等）",
       "modelSection": "模型配置",
-      "primaryModel": "主模型",
-      "primaryModelHint": "在供应商列表中通过「设为默认模型」按钮设置",
+      "primaryModel": "默认模型",
+      "primaryModelHint": "从已配置供应商的模型中选择默认模型",
       "notSet": "未设置",
       "fallbackModels": "回退模型",
-      "fallbackModelsHint": "逗号分隔，按优先级排列",
+      "fallbackModelsHint": "当主模型不可用时，按优先级依次尝试以下回退模型",
+      "addFallback": "添加回退模型",
+      "noModels": "暂无已配置的供应商模型。请先添加 OpenClaw 供应商。",
+      "notInList": "{{value}} (供应商未配置)",
       "runtimeSection": "运行参数",
       "workspace": "工作区路径",
       "timeout": "超时时间（秒）",