Fill future-call gaps: timeouts, DB inspection, scheduling from an endpoint

[developerjamiu]

Demand

Kapa "Future Calls & Scheduling" cluster — 10 conversations / 7 users. (Reactive future calls are covered by PR #447.)

Problem

Unanswered in the docs:

• "Do future calls have a timeout?"
• "Can I see scheduled calls in the database?" (table name / structure / how to inspect)
• "Can I schedule a future call from an endpoint?" — only shown from within a FutureCall.
• When to use a future call vs an endpoint for periodic external-DB sync.

Scope

• 14-scheduling/01-setup.md: an explicit "schedule from an endpoint" example; clarify behavior when multiple calls share an identifier.
• Document timeout behavior and how to inspect scheduled calls in the database.

Verify before writing

• Future-call execution timeout behavior; the DB table name/structure for scheduled calls (confirm against source).