docs: make workspace getting started assistant-first

[Jammy2211]

Summary

• Put the PyAutoGalaxy AI Assistant first in the workspace Getting Started section.
• Present conversation agents and coding agents as two ways to use one assistant.
• Introduce the remaining resources as human-readable documentation and examples while preserving installation, Colab, notebook, and browsable-example routes.

Scripts Changed

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

Upstream PR

PyAutoLabs/PyAutoGalaxy#521

Test Plan

• git diff --check
• python .github/scripts/run_smoke.py
• Confirmed existing installation, Colab, notebook, and browsable-example links remain present
• Confirmed https://github.com/PyAutoLabs/autogalaxy_assistant is the intended canonical URL; its temporary 404 was explicitly accepted by the maintainer in PyAutoLens issue #645 pending assistant creation later today

Generated by the PyAutoLabs agent workflow.