Add current date to query rewrite and chat answer prompts

Summary

Add the current date as a template variable to both the query rewrite and chat answer prompts. This will help the LLM understand temporal context when answering questions like "What happened last week?" or "What are the current policies?"

Proposed Changes

1. Pass current_date (formatted as "February 3, 2026") to the query rewrite prompt (query_rewrite.system.jinja2)
2. Pass current_date to the chat answer prompt (chat_answer.system.jinja2)
3. Update the Jinja2 templates to include the date in the system message

Implementation Notes

• Use datetime.now().strftime("%B %d, %Y") for formatting
• Add current_date to system_template_variables in both chatreadretrieveread.py call sites
• Consider if the date should also be added to the agentic retrieval path in approach.py

Related

This was partially implemented but reverted from the Jinja2 migration PR to keep that change focused.