fix: replace SQLite DATETIME with PostgreSQL TIMESTAMP(3) in init migration

[OpensrcLord]

Summary

The init migration (20260221132622_init/migration.sql) was written in SQLite DDL using DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP. Since migration_lock.toml and schema.prisma both declare provider = "postgresql", a fresh prisma migrate deploy against a PostgreSQL database fails immediately with:

type "datetime" does not exist

This blocks all table creation (User, Stream, StreamEvent) on a clean Postgres deploy.

Fix

Replaced all 5 occurrences of DATETIME with TIMESTAMP(3) in the init migration — the correct Prisma-generated column type for DateTime fields on PostgreSQL. No other columns, tables, or indexes were changed.

Changed file

• backend/prisma/migrations/20260221132622_init/migration.sql

Verification

• No DATETIME references remain in any migration file
• Column types now match what Prisma generates for postgresql provider
• Subsequent migrations (pause fields, IndexerState, unique constraint, indexes) are unaffected
• Datasource provider remains postgresql

Fixes #828