Resolve emails to accounts

Resolves many email addresses to account ids within ONE tenant, case-insensitively, in a single query — the read an importer runs BEFORE it writes anything, so the operator can see and fix unmatched rows while nothing has happened yet. Read-only and idempotent. Every input line comes back with a verdict in the order it was sent, with the email echoed exactly as supplied so a caller can line the answer up against its own file: found (with account_id and active) or not_found. An account that exists but is inactive is still found — whether that disqualifies it is the caller's policy. An email belonging to ANOTHER tenant comes back not_found, exactly like one that exists nowhere: the tenant is the whole boundary. Cross-tenant callers MUST pass tenant_id; tenant-scoped callers may pass their own or omit it. At most 1000 emails per call.