fix: enhance pgmq.meta table validation checks

[devin-ai-integration]

Enhance pgmq.meta table validation checks

This PR enhances the validation checks in the pgmq.meta backfill migration to ensure:

• pgmq.meta is a regular table (not a view or materialized view)
• Required columns exist: queue_name, is_partitioned, is_unlogged, created_at
• No additional columns exist
• Insert statement only executes if all conditions are met

Testing

• Migration changes have been reviewed for SQL syntax and logic
• No manual testing performed as this is a migration file change

Link to Devin run: https://app.devin.ai/sessions/ba98449afedc4fe8af288d2f5ca92121

[devin-ai-integration]

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