feat: support jsonl object preview

[savvym]

Pull Request

Description

Add support for previewing .jsonl / NDJSON files in the object preview modal.

This change:

• recognizes .jsonl and .ndjson as previewable text files
• adds MIME inference for NDJSON content types
• keeps JSONL rendering in the existing text preview flow

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• Security fix

Testing

• Unit tests added/updated
• Manual testing completed

Commands executed:

pnpm install --frozen-lockfile
pnpm run type-check
pnpm lint
pnpm exec prettier --check components/object/preview-modal.tsx lib/mime-types.ts

Notes:

• pnpm lint completes with existing repository warnings outside the scope of this PR, including a pre-existing <img> warning in components/object/preview-modal.tsx.
• pnpm test:run is not available in the current upstream package.json.
• pnpm prettier --check . is not included here because current repository baseline contains unrelated formatting drift.

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes #

Screenshots (if applicable)

N/A

Additional Notes

JSONL files are treated as safe text previews, similar to JSON and CSV, with support for both extension-based and MIME-based detection.