refactor: make stream smoothing parameters configurable and add models cache invalidation

- Move stream smoothing parameters (chunk_size, delay_ms) to database config
- Remove hardcoded stream smoothing constants from StreamProcessor
- Simplify dynamic delay calculation by using config values directly
- Add invalidate_models_list_cache() function to clear /v1/models endpoint cache
- Call cache invalidation on model create, update, delete, and bulk operations
- Update admin UI to allow runtime configuration of smoothing parameters
- Improve model listing freshness when models are modified

src/api/admin/providers/models.py

@@ -9,6 +9,7 @@ from fastapi import APIRouter, Depends, Request
 from sqlalchemy.orm import Session, joinedload
 
 from src.api.base.admin_adapter import AdminApiAdapter
+from src.api.base.models_service import invalidate_models_list_cache
 from src.api.base.pipeline import ApiRequestPipeline
 from src.core.exceptions import InvalidRequestException, NotFoundException
 from src.core.logger import logger
@@ -419,4 +420,8 @@ class AdminBatchAssignModelsToProviderAdapter(AdminApiAdapter):
             f"Batch assigned {len(success)} GlobalModels to provider {provider.name} by {context.user.username}"
         )
 
+        # 清除 /v1/models 列表缓存
+        if success:
+            await invalidate_models_list_cache()
+
         return BatchAssignModelsToProviderResponse(success=success, errors=errors)