Fix multi-statement result export

[DhruvShah-Dev]

Summary

• enable export for active multi-statement result tabs
• export loaded multi-statement result rows directly so temp-table scripts can be saved without rerunning on a new connection
• select the first result-bearing statement after batch execution and add formatter coverage for CSV, JSON, and Markdown exports

Fixes #627

Validation

• pnpm.cmd exec vitest run tests/utils/resultExport.test.ts tests/utils/multiResult.test.ts
• pnpm.cmd typecheck
• pnpm.cmd lint

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (3 files)

• src/pages/Editor.tsx
• src/utils/resultExport.ts
• tests/utils/resultExport.test.ts

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_{Reviewed by glm-5.2 · Input: 49.1K · Output: 15.2K · Cached: 336.4K}