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/zh.ts

@@ -114,6 +114,16 @@ export default {
   // 对话
   chat: {
     contextRemaining: '剩余',
+    contextClickToEdit: '点击编辑上下文长度',
+    contextEditTitle: '编辑上下文长度',
+    contextEditDesc: '设置当前模型的上下文长度限制（token 数量）',
+    contextEditPlaceholder: '请输入上下文长度',
+    contextEditHint: '常见值：200k (Claude), 128k (GPT-4), 32k (GPT-3.5)',
+    contextEditSave: '保存',
+    contextEditCancel: '取消',
+    contextEditInvalid: '请输入有效的上下文长度',
+    contextEditSuccess: '上下文长度已更新',
+    contextEditFailed: '更新失败',
     emptyState: '开始与 Hermes Agent 对话',
     inputPlaceholder: '输入消息... (Enter 发送，Shift+Enter 换行)',
     attachFiles: '添加附件',