Standardize talk README, presenter details, and slide downloads

[codebytes]

Summary

• Standardize the short talk README with HTML/PDF links, repository-specific resources, and canonical presenter contacts. Preserve all existing technical resource URLs and the MIT license section; link the slide source, workshop, and examples without adding an unnecessary guide.
• Link Mastodon in the speaker bio and closing resources slide. Preserve the current Principal Software Engineer bio, layout, and historical struck-through Twitter references.
• Add build/Slides.pdf to the existing Pages artifact using the same Marp image, input, theme, and HTML support, with local assets enabled. Existing publishing actions are already current and remain unchanged, as do asset copying, permissions, concurrency, and main/manual triggers. No teaching/example workflows or code changed.

Verification

• Started from a clean, freshly fetched origin/main at d6bc974.
• Passed actionlint, YAML/publishing-invariant checks, README/local-link/resource-preservation checks, and CRLF-aware whitespace checks. All three retained external resource URLs returned HTTP 200.
• Local Marp 4.5.0 rendered 41-slide HTML and a 41-page PDF. Checked the PDF title and Mastodon link annotations; visually inspected presenter slides 2 and 40, both with zero measured overflow.
• Full-deck overflow results exactly match the default-branch baseline: slides 14/16/19 overflow vertically by 49/65/55 px. These pre-existing teaching-slide issues are unchanged and outside scope.

Deployment note

The HTML URL is live. https://chris-ayers.com/github-actions-demos/Slides.pdf currently returns 404 and becomes available only after this PR is merged and the Pages workflow deploys. No production deployment or repository setting change was performed.