refactor: migrate email-worker to use shared-code package

Update email-worker to use @evidencija-rezija/shared-code for common types
and utilities instead of maintaining duplicate copies.

Changes:
- Add shared-code dependency to package.json
- Update imports in emailSenders.ts to use shared-code
- Remove duplicate db-types.ts and shareChecksum.ts files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

email-worker/package.json

@@ -12,6 +12,7 @@
   "author": "Nikola",
   "license": "ISC",
   "dependencies": {
+    "@evidencija-rezija/shared-code": "^1.0.0",
     "debug": "^2.6.9",
     "express": "^4.18.2",
     "form-data": "^4.0.5",