Feature: Scheduled orders with release semantics

[khaira777]

Feature: Scheduled orders with release semantics

Summary

Support orders scheduled for a future time (e.g. tomorrow 5pm). Today creating an order immediately marks it pending, deducts inventory (main/routes/orders.ts ~556/767) and notifies KDS — so adding a bare scheduled_for column would let the kitchen see tomorrow's pizza today.

Proposed approach

Keep scheduling separate from kitchen state:

orders: scheduled_for, release_status (scheduled|released), released_at

Flow: Customer places order → sits in scheduled queue → at release time it becomes a normal pending order → KDS.

• A background timer releases due orders; on startup, release any overdue orders in case the app was closed when the timer should have fired.
• One explicit product decision required (do not invent): does inventory get reserved at scheduling time or at release time?

Acceptance criteria

• Future orders appear in a scheduled view, not KDS.
• At release time the order becomes pending and KDS/inventory behavior matches today's flow exactly.
• Restarting the app while scheduled orders are due releases them.
• Fresh + upgrade-path DB tests (PRAGMA user_version migration; see AGENTS.md data-safety rules).