The Task 3 schema drifted from what better-auth@1.6.18's CLI generates: it used
mode:'timestamp' (epoch seconds) instead of 'timestamp_ms', left verification
timestamps nullable, and omitted the default expressions and helper indexes.
Regenerated src/db/schema.ts from `@better-auth/cli generate` (authoritative per
the plan's version-drift rule) and rebuilt migration 0000 from scratch (no data
exists yet). Converted the index callbacks from the CLI's array form to the
object form required by drizzle-orm@0.36.4's types. Adds session_userId_idx,
account_userId_idx, verification_identifier_idx and the unixepoch defaults.
Tests (health, db, auth sign-up/sign-in, /api/me round-trip) all pass; typecheck
clean; db:generate reports no pending changes.
