chore: remove unused ensureContactAssignment helper

[detail-app]

Removed ensureContactAssignment from contact.service.ts and dropped the
now-stale specific reference to it in the requireSendAccess doc comment
in send-access.service.ts (the general warning against pre-transaction
assignment claims is kept).

The function had zero production callers: it was the original "auto-assign
on first reply" mechanism, later superseded by requireSendAccess, which
migrated every call-site (send.ts, scheduled.ts, conversations/messages.ts)
but left the definition behind. The send-access warning comment explicitly
told callers NOT to use it, and leaving it in place would mislead by
looking like a simpler alternative to the lock-aware guard while
reintroducing the TOCTOU race SLA enforcement was built to close.

History

• Last materially changed January 2026 (@setkyar)

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