feat: Add script for migrating data from CockroachDB to SQLite

[KallynGowdy]

Adds npm run migrate:cockroachdb-to-sqlite, which copies every row from
a CockroachDB database into a SQLite database. Both databases are expected
to already have all of their migrations applied - the script only moves
data and never touches DDL or _prisma_migrations.

The copy plan is derived at runtime from the DMMF of both generated Prisma
clients, so all 68 models are covered without a hand-written mapping and
the script stays in sync as the schemas change. It applies the differences
between auth.prisma and auth.sqlite.prisma:

• DateTime columns become epoch milliseconds (Decimal), matching
  convertToMillis() in aux-backend/prisma/Utils.ts.
• String[] columns become JSON arrays.
• Json nulls are written as Prisma.JsonNull/Prisma.DbNull depending
  on whether the target column is nullable.
• BranchUpdate.updated maps to BranchUpdate.updatedAt.
• Rows whose value is null in a column the SQLite schema requires (i.e.
  Invoice.subscriptionId) are skipped and reported.

Rows are read with keyset pagination ordered by primary key so large
tables don't slow down as the copy progresses, and written with
createMany in chunks sized to stay under SQLite's parameter limit.
Models are inserted in dependency order with PRAGMA foreign_keys = OFF,
since the schema contains two genuine foreign key cycles
(User <-> LoginRequest and Record -> FinancialAccount -> ContractRecord).
PRAGMA foreign_key_check runs at the end and a non-empty result exits
non-zero.

The script refuses to run against a non-empty target unless --truncate
or --skip-duplicates is given, and supports --dry-run, --only,
--exclude, --batch-size, and --yes.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01GRQLzHumoQT9P6zwiNQFyV

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