Standardize julia & datascience lecture repo names (lecture-<topic>, drop .myst)

[mmcky]

Standardize julia & datascience lecture repo names (lecture-<topic>, drop .myst)

Companion to the core-series rename in #333, split out because lecture-julia.myst and lecture-datascience.myst are maintained by Jesse Perla as a separate process. Filing this so the direction is tracked; the decision and timing rest with that team.

Proposal (for that team to confirm)

Drop the vestigial .myst suffix so these align with the lecture-<topic> pattern most repos already follow:

Current repo	Site (unchanged)	→ New repo	Series
lecture-julia.myst	julia.quantecon.org	lecture-julia	Quantitative Economics with Julia
lecture-datascience.myst	datascience.quantecon.org	lecture-datascience	Data Science

Both target names are currently free.

No companion churn

The .notebooks companions never carried the .myst suffix, so they already conform and need no change:

• lecture-julia.notebooks ✅
• lecture-datascience.notebooks ✅

Scope constraint — no hosting changes

Repository-rename-only. Custom domains, GitHub Pages configuration, Netlify deploys, and HTTPS all stay exactly as they are — julia.quantecon.org and datascience.quantecon.org keep serving unchanged. Renaming a GitHub repo does not touch its Pages custom domain or CNAME, and GitHub auto-redirects the old repo URL and git remotes.

Per-repo rollout (when that team is ready)

• Rename the repo in Settings (GitHub creates automatic redirects)
• Update in-repo references (publish.yml release-asset name + notebook-sync destination, _config.yml, notebook download links, README badges)
• Confirm Netlify deploy still works (no changes needed)
• Verify the custom domain is still serving (CNAME + Pages config unaffected)
• Notify contributors to update local remotes (git remote set-url …)