feat: Add agent module for shared utilities

[haroon0x]

Summary

Adds an agent/ module to centralize shared utilities, preparing the codebase for agentic workflows.

Changes

• agent/config.py - Centralized environment variables
• agent/prompts.py - System prompt and tool definitions
• agent/rag.py - Milvus search and tool execution

Motivation

This prepares for the GSoC Agentic RAG proposal by making tool definitions modular and reusable.

Future Work

• Update server-https/app.py to import from agent/

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign franciscojavierarceo for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment