fix: remove driver packages from root/opencode deps to fix 4x binary bloat

Driver packages (snowflake-sdk, @databricks/sql, @google-cloud/bigquery,
pg, mysql2, mssql) were in root and opencode package.json causing esbuild
to bundle them into binaries — inflating from 1GB to 4GB.

Fix: removed from root/opencode. They remain in packages/drivers as
optionalDependencies. Drivers load lazily via dynamic import() at runtime.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: anandgupta42