fix(csv-to-pg): emit empty array '{}' instead of NULL for array types

[pyramation]

Summary

When array-typed columns (jsonb[], uuid[], text[]) have null or empty values, csv-to-pg now emits '{}' (empty PostgreSQL array literal) instead of SQL NULL. This fixes NOT NULL constraint violations when exported SQL is deployed to databases where array columns have NOT NULL defaults (e.g. secure_table_provision.fields and secure_table_provision.grant_privileges).

csv-to-pg/src/parse.ts: makeNullOrThrow now returns '{}' for any array type instead of NULL when the value is missing/empty. psqlArray also returns '{}' for empty arrays instead of undefined. A new isArrayType helper detects array types by checking for trailing [].

Two new test cases verify null and empty array inputs both emit '{}' instead of NULL.

Updates since last revision

• Removed the redundant COALESCE fix from pgpm/export/src/export-meta.ts — the csv-to-pg serialization layer now handles this, so the query-level workaround is unnecessary.

Review & Testing Checklist for Human

• Breaking change risk on makeNullOrThrow: This changes behavior for ALL array types across ALL consumers of csv-to-pg, not just the export pipeline. Verify no existing consumer relies on getting SQL NULL for empty/missing array columns. If any table legitimately needs NULL arrays, this would silently change the semantics.
• End-to-end test: Run a full provision → export → deploy cycle on agentic-db (or any project) to confirm the exported SQL deploys cleanly without the manual NULL → '{}' post-processing workaround.

Notes

• The psqlArray change (empty array → '{}' instead of undefined) also affects the text[] handler path, which calls psqlArray directly before checking emptiness.
• This was the root cause of repeated CI failures in agentic-db PR #30 where pgpm-deploy failed with null value in column "fields" violates not-null constraint.

Link to Devin session: https://app.devin.ai/sessions/f72c3360c9494043aa60d59ff302be83
Requested by: @pyramation

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