Fix op checkpoint JSONB array binding

[EagleEyez1]

Summary

Fixes a live Postgres sync failure where recordCompleted() wrote completed_keys as a JSON string instead of a JSON array through a postgres.js unsafe placeholder.

In production this surfaced as:

new row for relation "op_checkpoints" violates check constraint "op_checkpoints_completed_keys_array"

The database constraint was correct; the writer was double-encoding the value by passing JSON.stringify(sorted) to $3::jsonb.

Change

• Pass the JavaScript string[] directly to the $3::jsonb placeholder.
• Keep the defensive fallback as an empty JavaScript array.
• This preserves the v119 completed_keys array-shape guard and lets postgres.js serialize the JSONB value correctly.

Validation

bun test test/op-checkpoint*.test.ts
37 pass
0 fail

Also validated against the production Artie brain after the same fix:

• gbrain sync --no-pull --no-embed completed successfully after previously aborting before import.
• gbrain embed --stale restored missing embeddings to 0.
• Retrieval gate remained healthy.