refactor(llm): enhance RAG and LLM debug logging for observability

[marevol]

Summary

Enhance RAG and LLM logging to improve observability and debugging capabilities.

Changes Made

• ChatClient: Add info-level log for search phase completion with query, result count, and elapsed time; include userId in enhanced chat completion log
• AbstractLlmClient: Add debug-level logs for concurrency permit acquisition (available permits, max concurrent), LLM response token usage (prompt/completion/total tokens, finish reason) for intent and evaluation phases, and history inclusion details (count, start index, character budget)
• LlmClientManager: Simplify redundant debug log messages that duplicate information already logged at lower levels

Testing

• Logging changes only; no behavioral impact
• Verified compilation

Additional Notes

• Follows existing [RAG]/[LLM] prefix conventions established in refactor(llm): improve RAG and LLM logging with consistent prefixes and levels #3070
• New detailed logs use debug level to avoid noise in production