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",

email-worker/src/lib/emailSenders.ts

@@ -1,6 +1,5 @@
 import { Db, ObjectId } from 'mongodb';
-import { BillingLocation, EmailStatus, UserSettings } from '../types/db-types';
-import { generateShareId } from './shareChecksum';
+import { BillingLocation, EmailStatus, UserSettings, generateShareId } from '@evidencija-rezija/shared-code';
 import { sendEmail } from './mailgunService';
 import { createLogger } from './logger';
 

email-worker/src/lib/shareChecksum.ts

@@ -1,36 +0,0 @@
-import crypto from 'crypto';
-
-/**
- * Checksum length in hex characters (16 chars = 64 bits of entropy)
- */
-export const CHECKSUM_LENGTH = 16;
-
-/**
- * Generate share link checksum for location
- * Uses HMAC-SHA256 for cryptographic integrity
- *
- * SECURITY: Prevents location ID enumeration while allowing stateless validation
- */
-export function generateShareChecksum(locationId: string): string {
-    const secret = process.env.SHARE_LINK_SECRET;
-
-    if (!secret) {
-        throw new Error('SHARE_LINK_SECRET environment variable not configured');
-    }
-
-    return crypto
-        .createHmac('sha256', secret)
-        .update(locationId)
-        .digest('hex')
-        .substring(0, CHECKSUM_LENGTH);
-}
-
-/**
- * Generate combined location ID with checksum appended
- * @param locationId - The MongoDB location ID (24 chars)
- * @returns Combined ID: locationId + checksum (40 chars total)
- */
-export function generateShareId(locationId: string): string {
-    const checksum = generateShareChecksum(locationId);
-    return locationId + checksum;
-}

email-worker/src/types/db-types.ts

@@ -1,54 +0,0 @@
-import { ObjectId } from 'mongodb';
-
-export interface YearMonth {
-    year: number;
-    month: number;
-}
-
-export enum EmailStatus {
-    /** Email is not yet verified - recipient has not yet confirmed their email address */
-    Unverified = "unverified",
-    /** Email is not yet verified - a verification request has been sent */
-    VerificationPending = "verification-pending",
-    /** sending of verification email failed */
-    VerificationFailed = "verification-failed",
-    /** Email is verified and is in good standing: emails are being successfully delivered */
-    Verified = "verified",
-    /** Recepient has unsubscribed from receiving emails via link - no further emails will be sent */
-    Unsubscribed = "unsubscribed"
-}
-
-/** User settings data */
-export interface UserSettings {
-    /** user's ID */
-    userId: string;
-    /** owner name */
-    ownerName?: string | null;
-}
-
-/** Billing location document from MongoDB */
-export interface BillingLocation {
-    _id: ObjectId;
-    /** user's ID */
-    userId: string;
-    /** name of the location */
-    name: string;
-    /** billing period year and month */
-    yearMonth: YearMonth;
-    /** (optional) tenant name */
-    tenantName?: string | null;
-    /** (optional) tenant email */
-    tenantEmail?: string | null;
-    /** (optional) tenant email status */
-    tenantEmailStatus?: EmailStatus | null;
-    /** (optional) whether to automatically notify tenant */
-    billFwdEnabled?: boolean | null;
-    /** (optional) bill forwarding status */
-    billFwdStatus?: "pending" | "sent" | "failed" | null;
-    /** (optional) whether to automatically send rent notification */
-    rentDueNotificationEnabled?: boolean | null;
-    /** (optional) day of month when rent is due (1-31) */
-    rentDueDay?: number | null;
-    /** (optional) when was the rent due notification sent */
-    rentDueNotificationStatus?: "sent" | "failed" | null;
-}