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/en.ts

@@ -114,6 +114,16 @@ export default {
   // Chat
   chat: {
     contextRemaining: 'remaining',
+    contextClickToEdit: 'Click to edit context length',
+    contextEditTitle: 'Edit Context Length',
+    contextEditDesc: 'Set context length limit for current model (in tokens)',
+    contextEditPlaceholder: 'Enter context length',
+    contextEditHint: 'Common values: 200k (Claude), 128k (GPT-4), 32k (GPT-3.5)',
+    contextEditSave: 'Save',
+    contextEditCancel: 'Cancel',
+    contextEditInvalid: 'Please enter a valid context length',
+    contextEditSuccess: 'Context length updated',
+    contextEditFailed: 'Update failed',
     emptyState: 'Start a conversation with Hermes Agent',
     inputPlaceholder: 'Type a message... (Enter to send, Shift+Enter for new line)',
     attachFiles: 'Attach files',