feat(schedules): hand the katoptra mirrors to katoptra/dispatch

[jshvn]

Summary

• Removes the four katoptra schedules (ctan, dropbox, github, tlnet). They now live in katoptra/dispatch, on bendalloy.jgrid.net.
• wrangler.jsonc triggers go from four crons to one, 17 5 * * * (evening), for terraform's drift.yml, which is now the only target.
• The README's schedule example now uses the terraform file.

Test plan

• task crons regenerated the triggers
• task check: types, format, tests, dry-run deploy
• after merge, deploy.yml redeploys; npx wrangler triggers or the dashboard shows one cron
• tomorrow at 05:17 UTC, terraform's drift.yml still runs from workflow_dispatch