Fix SQL Editor export row limit

[intraq-dev-ai]

Summary

• Keep SQL Editor preview queries capped at 1,000 rows
• Rerun the last successful SQL Editor query for CSV export with a 100,000-row cap
• Raise backend configurable query cap so export-sized SQL Editor requests can exceed preview limits
• Document SQL Editor preview/export row limits
• Add smoke tests for frontend limit payloads and sample-data export-sized limits

Fixes #9

Validation

• npx vitest run tests/smoke/sql-editor-export-limits.test.ts
• npm test
• docker run --rm -v /Users/anupnepal/projects/intraQ/intraq-community:/work -v intraq-community-node24-modules:/work/node_modules -w /work node:24-alpine sh -lc 'npm run build'