chore(server/llm): switch default doubao model to seed-2-0-pro

Bump the default LLM from doubao-seed-2-0-lite to doubao-seed-2-0-pro
for higher-quality completions on tenant-side LLM calls; keep the lite
id in a trailing comment for quick rollback.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/configs/config.yaml

@@ -147,7 +147,7 @@ llm:
   provider: ark
   base_url: https://ark.cn-beijing.volces.com/api/v3
   api_key: "7fb6c66b-129c-4935-9617-709236c4205a"
-  model: doubao-seed-2-0-lite-260215   #
+  model: doubao-seed-2-0-pro-260215 # doubao-seed-2-0-lite-260215   #
   knowledge_url_model: doubao-seed-2-0-mini-260215 #doubao-seed-2-0-mini-260215
   timeout: 2m
   max_output_tokens: 16000