feat: Add email configuration and alert system

Introduces SMTP configuration settings and alert definitions to enable automated email notifications.
This includes new types for `SmtpConfig` and `AlertDefinition`, and integrates these into the settings page and mock database.
Adds styling for select elements and scrollbar hiding in the main HTML.
Updates mock database logic to potentially support local development without a backend.

types.ts

@@ -16,10 +16,31 @@ export interface Payment {
   notes?: string;
 }
 
+export interface SmtpConfig {
+  host: string;
+  port: number;
+  user: string;
+  pass: string;
+  secure: boolean;
+  fromEmail: string;
+}
+
+export interface AlertDefinition {
+  id: string;
+  subject: string;
+  body: string;
+  daysOffset: number; // Number of days
+  offsetType: 'before_next_month' | 'after_current_month';
+  sendHour: number; // 0-23
+  active: boolean;
+  lastSent?: string; // ISO Date of last execution
+}
+
 export interface AppSettings {
   defaultMonthlyQuota: number;
   condoName: string;
   currentYear: number; // The active fiscal year
+  smtpConfig?: SmtpConfig;
 }
 
 export enum PaymentStatus {
@@ -42,6 +63,7 @@ export interface User {
   role?: 'admin' | 'poweruser' | 'user';
   phone?: string;
   familyId?: string | null;
+  receiveAlerts?: boolean;
 }
 
 export interface AuthResponse {