feat: Add database table for model context length configuration (#477)

* feat: add database table for model context length configuration

- Add model_context table with provider/model/context_limit fields
- Implement UPSERT endpoint for model context configuration
- Add priority lookup: database > config.yaml > custom_providers > cache
- Add frontend click-to-edit UI in ChatInput with tooltip
- Add i18n support for context editing dialog (all 8 locales)
- Use context_limit field consistently across frontend and backend

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: use useMessage() composable instead of window.$message in ChatInput

- Remove incorrect NMessage import (not a component)
- Use useMessage() composable from naive-ui
- Replace window.$message?.xxx() with message.xxx()
- Fixes TypeScript build errors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/client/src/i18n/locales/ja.ts

@@ -104,6 +104,16 @@ export default {
   // チャット
   chat: {
     contextRemaining: '残り',
+    contextClickToEdit: 'クリックしてコンテキスト長を編集',
+    contextEditTitle: 'コンテキスト長を編集',
+    contextEditDesc: '現在のモデルのコンテキスト長制限を設定（トークン数）',
+    contextEditPlaceholder: 'コンテキスト長を入力',
+    contextEditHint: '一般的な値：200k (Claude), 128k (GPT-4), 32k (GPT-3.5)',
+    contextEditSave: '保存',
+    contextEditCancel: 'キャンセル',
+    contextEditInvalid: '有効なコンテキスト長を入力してください',
+    contextEditSuccess: 'コンテキスト長を更新しました',
+    contextEditFailed: '更新に失敗しました',
     emptyState: 'Hermes Agent と会話を開始しましょう',
     inputPlaceholder: 'メッセージを入力... (Enter で送信、Shift+Enter で改行)',
     attachFiles: 'ファイルを添付',