Update memory docs to use Agent Factory pattern

[aidandaly24]

Description

The memory documentation currently describes a non-sessionful setup. It should be updated to use the Agent Factory method, which provides a better, session-aware memory integration for Strands agents.

Category

Documentation

Acceptance Criteria

• Update memory docs to use the Agent Factory pattern as described in docs/memory.md
• Ensure the documented approach produces a sessionful agent
• Align with the changes from PR Make Strands template Agent sessionful #216

Additional Context

• Reference PR: Make Strands template Agent sessionful #216 (Make Strands template Agent sessionful)
• Reference docs: memory.md — Adding memory to an agent without memory (Strands)

[notgitika]

closed by: #280