Add models for EmailTemplate, ActivityLog, and NotificationLog

Introduced new database models to handle email templates, activity logs, and notification logs, including relevant enums and utilities. Updated ER diagram to reflect new relationships and attributes, enhancing event tracking and notification management capabilities.

docs/eventspace-er-schema.mermaid

@@ -2,6 +2,8 @@ erDiagram
     User ||--o{ Event : "creates"
     User ||--o{ EventManager : "is assigned as"
     User ||--o{ Guest : "can be linked to"
+    User ||--o{ ActivityLog : "generates"
+    User ||--o{ EmailTemplate : "creates"
     User {
         uuid id PK
         string email UK
@@ -37,6 +39,9 @@ erDiagram
     Event ||--o{ GiftItem : "contains"
     Event ||--o{ EventMedia : "has"
     Event ||--o{ GiftCategory : "has"
+    Event ||--o{ EmailTemplate : "has"
+    Event ||--o{ NotificationLog : "generates"
+    Event ||--o{ ActivityLog : "tracks"
     Event }o--|| EventTheme : "uses"
     Event {
         uuid id PK
@@ -70,6 +75,8 @@ erDiagram
 
     Guest ||--o{ RSVP : "submits"
     Guest ||--o{ GiftPurchase : "makes"
+    Guest ||--o{ NotificationLog : "receives"
+    Guest ||--o{ ActivityLog : "generates"
     Guest {
         uuid id PK
         uuid event_id FK
@@ -195,5 +202,60 @@ erDiagram
         datetime updated_at
     }
 
+    EmailTemplate {
+        uuid id PK
+        string name
+        string description
+        enum template_type "INVITATION/REMINDER/CONFIRMATION/UPDATE/THANK_YOU/CUSTOM"
+        string subject
+        text html_content
+        text text_content
+        json variables
+        uuid event_id FK "nullable"
+        uuid created_by FK
+        boolean is_active
+        boolean is_system
+        datetime created_at
+        datetime updated_at
+    }
+
+    NotificationLog {
+        uuid id PK
+        enum notification_type "EMAIL/SMS/PUSH/IN_APP"
+        enum status "QUEUED/SENT/DELIVERED/FAILED/OPENED/CLICKED"
+        string subject
+        string content_preview
+        uuid template_id FK
+        uuid event_id FK
+        uuid guest_id FK "nullable"
+        string recipient
+        datetime sent_at
+        datetime delivered_at
+        datetime opened_at
+        string error_message
+        integer retry_count
+        string external_id
+        json metadata
+        datetime created_at
+        datetime updated_at
+    }
+
+    ActivityLog {
+        uuid id PK
+        enum activity_type
+        text description
+        uuid event_id FK "nullable"
+        uuid user_id FK "nullable"
+        uuid guest_id FK "nullable"
+        uuid target_id "generic ID"
+        string target_type "type of target"
+        string ip_address
+        string user_agent
+        json data
+        datetime created_at
+        datetime updated_at
+    }
+
+    EmailTemplate }o--|| NotificationLog : "used for"
     User ||--o{ EventManager : "has roles"
     Event ||--o{ RSVP : "receives"