docs: make workspace getting started assistant-first

[Jammy2211]

Summary

• Put the PyAutoLens AI Assistant first in the workspace Getting Started section.
• Present conversation agents and coding agents as two ways to use one assistant.
• Remove the duplicated “Three Ways to Learn PyAutoLens” section while preserving installation, Colab, notebook, and browsable-example routes.

Scripts Changed

• None — this is a root README.md documentation change only.

Upstream PR

PyAutoLabs/PyAutoLens#646

Test Plan

• git diff --check
• python .github/scripts/run_smoke.py
• Confirmed existing installation, Colab, notebook, and browsable-example links remain present
• Confirmed the retired chat/agentic/Three Ways terminology is absent from README.md

Generated by the PyAutoLabs agent workflow.