[WIP] Add ability to hide lookup IDs on link lines

[Copilot]

Summary

This PR adds a new setting to hide lookup IDs on relationship link labels and ensures the option is preserved across Draw.io export and shared URLs.

What changed

• Added showRelationshipLookupIds support in src/types/erdTypes.ts
• Added Draw.io export behavior to omit lookup IDs when disabled in src/utils/drawioExport.ts
• Extended URL share state encoding/decoding in src/utils/urlStateCodec.ts
• Restored the setting from shared URLs in src/App.tsx
• Parsed the new checkbox setting correctly in src/types/erdTypes.ts
• Updated the sidebar setting documentation in README.md
• Added regression tests for Draw.io export and URL state handling

Verification

• `npm run test:run -- src/utils/tests/urlStateCodec.test.ts src/utils/tests/drawioExport.test.ts`
• Result: `110 passed`