Use Pydantic AI for LLM chat

[DavidMStraub]

Groundwork for tool calling in AI chat, see #586.

[DavidMStraub]

@MPietrala FYI, I have tried reimplementing the chat endpoint using Pydantic AI, with the existing RAG functionality as a tool.

It seems to work!

Let me know if you have any comments.

[Copilot]

Pull Request Overview

This PR migrates the LLM chat functionality from using OpenAI's Python SDK directly to using Pydantic AI, a framework that provides structured agent-based interactions with LLMs. The migration introduces tool-based function calling capabilities and improves the overall architecture of AI interactions.

• Replaced direct OpenAI client usage with Pydantic AI agent framework
• Introduced new tool-based architecture with get_current_date and search_genealogy_database tools
• Updated dependencies to use pydantic-ai[openai]>=1.0.0 instead of standalone openai package

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pyproject.toml	Updated AI dependencies: added pydantic-ai[openai]>=1.0.0, added version constraint to sentence-transformers, removed boto3 version constraint, removed standalone openai package
gramps_webapi/api/resources/chat.py	Changed function call from answer_prompt_retrieve to answer_with_agent and improved error message to include exception details
gramps_webapi/api/llm/init.py	Added new answer_with_agent function with Pydantic AI agent support, message history conversion, moved raise statement, renamed variable from total to _, added docstring to answer_prompt_retrieve
gramps_webapi/api/llm/deps.py	New file defining AgentDeps dataclass for agent dependencies
gramps_webapi/api/llm/agent.py	New file defining agent creation logic with system prompt and tool registration
gramps_webapi/api/llm/tools.py	New file defining Pydantic AI tools: get_current_date and search_genealogy_database with logging decorator
tests/test_endpoints/test_chat.py	Updated test to mock create_agent instead of OpenAI client, simplified mock structure

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