[Tech-debt] Decide orgHandle immutability vs migrate child FKs to surrogate orgUID

[Salem874]

Problem

Core FKs (tblUsers, tblOrgDomains, tblOrgShortDomains, tblOrgInvitations, tblUserAccountTypes, …) target the mutable business key orgHandle rather than a surrogate orgUID. Handle renames cascade across all child tables and couple everything to a mutable string.

Decision needed (pre-launch — cheap now, expensive after data grows)

Either (a) formally document orgHandle as immutable (keep ON UPDATE CASCADE as a safety net), or (b) migrate child FKs to orgUID.

Acceptance criteria

• Decision recorded in DATABASE.md; schema/docs consistent.

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From the 2026-06-04 schema review — see docs/SCHEMA_REVIEW_2026-06-04.md.