docs(skills): teach the calendar-hours rule where a hook stamps a deadline

The data-hooks sandbox section now carries the hook-deadline rule: a deadline
stamped from an hours table is calendar hours, the table is named
`*_CALENDAR_HOURS` (or its camelCase), the arithmetic adds elapsed milliseconds,
and wall-clock arithmetic is never labelled "business hours".

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018dxq7YqsLDMeZDZ5AzsgJX

Author: claude

skills/objectstack-data/references/data-hooks.md

@@ -452,6 +452,10 @@ The body runs in an isolated QuickJS VM, **not** Node:
   the hook. A `body` must be **self-contained**: inline the helper, or keep that
   hook as a bundled `handler`.
 
+> **A deadline stamped from an hours table is calendar hours** — nights, weekends and
+> holidays count. Name it `SLA_CALENDAR_HOURS` (or its camelCase) and add elapsed
+> milliseconds (`hours * 3_600_000`); never label it "business hours".
+
 ### ⚠️ Gotcha 1 — `ctx.result` is a *partial* record on afterUpdate
 
 On `afterUpdate`, both `ctx.result` and `ctx.input` carry only the fields this