feat: update requesters and improve provider selection UI

- Added `litellm_provider` field to various requesters' YAML configurations.
- Removed obsolete Python requester files for OpenRouter, PPIO, QHAIGC, ShengSuanYun, SiliconFlow, Space, TokenPony, VolcArk, and Xai.
- Introduced new requesters for Tencent and Together AI with corresponding YAML configurations and SVG icons.
- Enhanced the ProviderForm component to include a searchable dropdown for selecting providers, improving user experience.
- Updated localization files to include search provider text for both English and Chinese.

src/langbot/pkg/provider/modelmgr/requesters/modelscopechatcmpl.yaml

@@ -7,6 +7,7 @@ metadata:
     zh_Hans: 魔搭社区
   icon: modelscope.svg
 spec:
+  litellm_provider: openai
   config:
   - name: base_url
     label:
@@ -31,6 +32,8 @@ spec:
     default: 120
   support_type:
   - llm
+  - text-embedding
+  - rerank
   provider_category: maas
 execution:
   python: