[Improvement] Deduplicate export logic between ExportPanel.tsx and CLI

[d-oit]

Description

The export logic is fully duplicated between src/features/export/ExportPanel.tsx and cli/index.ts. Both implement Markdown, JSON, and HTML site export independently with slightly different behavior and different security postures.

Duplication

Feature	ExportPanel.tsx	cli/index.ts
Markdown export	✅ Single file	✅ Per-entity files
JSON export	✅ Single file	✅ Single file
HTML site export	✅ Single file	✅ Single file
HTML escaping	Partial (names only)	None
Shared logic	None	None

Recommended Fix

1. Extract shared export logic into src/lib/export/ module
2. Create format-specific exporters: MarkdownExporter, JsonExporter, HtmlSiteExporter
3. Use the shared module from both browser and CLI
4. Ensure consistent security posture (escaping) across both paths

Acceptance Criteria

• Export logic extracted to shared module
• Both browser and CLI use shared exporters
• Consistent HTML escaping across both paths
• No duplicated export code