Stream large database exports

[anshumanjaiswal]

Purpose

Closes #59 by streaming internal database exports in bounded pages instead of loading the entire SQL dump, JSON export, or CSV export into memory before responding.

Tasks

• Add pull-driven text streaming helper for exports
• Page table reads with a bounded, configurable batch size
• Stream SQL dump, JSON, and CSV exports
• Preserve CSV/SQL escaping and quote table identifiers safely
• Add export tests for streaming, pagination, empty tables, and escaping

Verify

• npm test -- --run src/export
• npm run build

Before

Export routes constructed the full export body in memory before returning a response.

After

Export routes return a ReadableStream and fetch rows page-by-page as the client consumes the download.

[anshumanjaiswal]

/claim #59