docs: update operations.md to reflect D1 → PlanetScale PostgreSQL migration (#25)

Update all references from D1/SQLite to Hyperdrive/PlanetScale PostgreSQL
following the platform database migration (PR #21). Changes include:
resource tables, deploy scripts, fresh environment setup, token permissions,
and a new Migration History section with a comprehensive before/after table.
Also tick off the migration item in progress.md.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: Brooooooklyn