Update main.ts to automatically generate API keys on first load,
encrypt them when saving to disk, and decrypt them when loading.
Also migrate legacy settings by removing enableCORS and
allowedOrigins fields.
Changes:
- Auto-generate API key if empty on plugin load
- Encrypt API key before saving to data.json
- Decrypt API key after loading from data.json
- Migrate legacy settings by removing CORS-related fields
- Add imports for generateApiKey, encryptApiKey, decryptApiKey
- Add comprehensive migration tests in main-migration.test.ts
This implements Task 4 of the CORS simplification plan.
