Align public export row caps

[intraq-dev-ai]

Summary

• Align chart export backend max with the public 100,000-row export cap.
• Make dashboard component download payloads request 100,000 rows instead of 1,000,000.
• Make embed data-source download cap 100,000 rows instead of 1,000,000.
• Align Analyzer export request constants with the same 100,000-row cap.
• Add smoke coverage to keep dashboard/embed/export constants aligned with SQL Editor export limit.

Issue

Fixes #16.

Validation

• npx vitest run tests/smoke/sql-editor-export-limits.test.ts
• npm run type-check --workspace @intraq/api
• npm test