Update Agent 365 implementation guide diagrams and remove Roadmap

[Alejandro Lopez (soyalejolopez)]

Summary

• Remove the Roadmap section, its navigation entry, and dedicated CSS from the Agent 365 customer implementation guide.
• Place the original Agent 365 Lifecycle Atlas hero first in the Diagrams section, with light and dark variants, source attribution, and an accessible enlargement dialog.
• Add "For more diagrams, click here" linking to https://aka.ms/fasttrackext/a365diagram.
• Preserve public-specific guide content. The comparison against microsoft/FastTrack master contains only five intended resource files.

Source and scope

Guide: https://aka.ms/fasttrackext/a365guide
Diagram source: https://microsoft.github.io/FastTrack/copilot-agent-strategy/agent-365-lifecycle-atlas/index.html#architecture
The hero uses the existing public atlas SVG source, not a recreated diagram. No private material or new roadmap claims are introduced.

Validation

• Catalog checks, JavaScript syntax, and git diff whitespace checks passed.
• Checked light/dark rendering at 320, 768, 1024, and 1440px widths.
• Checked dialog keyboard behavior, Escape, and focus handling.
• Verified embedded/source SVG fidelity and offline diagram rendering without network requests.
• Independent GPT-5.6 Sol review found no disclosure or correctness blockers after Claude Opus 4.8 implementation.

Reviewer notes

Target microsoft/FastTrack:master. Review the five-file upstream comparison, not the stale fork-default-branch comparison. This PR updates the guide only; merging and deployment remain maintainer actions.