feat(export): explicit excludeCategories filtering in exportMigrations

[pyramation]

Summary

Makes excludeCategories a real, first-class export filter in both export modes, replacing the inert cross-connection export.exclude_categories GUC approach.

SQL mode (exportMigrations / exportMigrationsToDisk): new excludeCategories?: string[] option filters directly in the exporter query (parameterized, null-preserving, deterministic):

select * from db_migrate.sql_actions
where database_id = $1
  and (category is null or category != ALL($2::text[]))
order by id

Also removes an incorrect pgPool.end() on the cached pool from getPgPool().

GraphQL mode (exportGraphQL): the migrate-client schema/ORM previously didn't expose category at all, so the GraphQL path couldn't filter. This PR:

• adds category to sdk/migrate-client/schemas/migrate.graphql (SqlAction, SqlActionFilter, SqlActionOrderBy) and regenerates the ORM client
• selects category and filters server-side in the sqlAction.findMany where-clause:

where: {
  databaseId: { equalTo: databaseId },
  or: [{ category: { isNull: true } }, { category: { notIn: excludeCategories } }]
}

CLI: pgpm export --exclude-categories security,permissions,auth,memberships now works in both SQL and GraphQL modes.

Behavior notes: omitted/empty excludeCategories preserves the original queries exactly; category IS NULL rows are always kept; ordering stays ID_ASC with existing pagination.

Testing

• pgpm/export integration tests extended with a category='security' action: excluded from plan/deploy files when filtered, retained when not — 146 tests passing.
• migrate-client, @pgpmjs/export, pgpm CLI build clean.

Link to Devin session: https://app.devin.ai/sessions/9ad75ab0ed7e412f9339213390ddf29a
Requested by: @pyramation

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