feat(schedules): register workflows in five named slots

[jshvn]

What

Replaces per-workflow cron strings with a SLOTS table of five named expressions in schedules/index.ts. A leaf declares slots: [...] and ends in as const, so a misspelt slot, a leaf without as const, or an empty slot list fails to compile on the registry line. Target keeps its cron, so src/index.ts is untouched.

slot	UTC	Pacific, winter
hourly	:42	:42
overnight	11:17	03:17
morning	17:17	09:17
afternoon	23:17	15:17
evening	05:17	21:17

One expression per slot rather than one four-hour daily: Cloudflare hands the Worker the same string for every hour a list expression matches, so a target could not pick one, and a dropped trigger takes one slot down rather than every daily. Only slots with a target become triggers; wrangler.jsonc carries three until morning or afternoon is claimed. Registering a workflow in a slot already in use no longer touches wrangler.jsonc, so it needs no task crons and has no propagation window.

Fire times move

• ctan stays hourly at :42.
• dropbox: 20 11 to 17 11, three minutes earlier.
• terraform: 15 4 to 17 5, about an hour later.
• tlnet: 30 3 to 17 5, about two hours later. It now shares a firing with terraform.

The three daily expressions are new strings, so each pays the 15-minute propagation delay once and may miss its first slot after deploy.

Test plan

• task check passes: typecheck, format, 45 tests, dry-run deploy
• A misspelt slot, a leaf without as const, and slots: [] each fail tsc on the REPOS line
• task crons run; wrangler.jsonc carries 17 11, 17 5, 42 *
• task targets prints the slot column
• After deploy, task instances shows the 17 5 * * * firing with two steps