Add attachment deletion route and automatic cleanup on record deletion

Co-authored-by: aiulian25 <17886483+aiulian25@users.noreply.github.com>

ATTACHMENT_API.md

@@ -85,6 +85,41 @@ Download or view an attachment.
 
 ---
 
+### Delete Attachment
+Delete an attachment file.
+
+**Endpoint:** `DELETE /api/attachments/delete`
+
+**Authentication:** Required
+
+**Query Parameters:**
+- `path` (required): Relative path to the attachment (e.g., `attachments/filename.pdf`)
+
+**Response:**
+```json
+{
+  "message": "Attachment deleted successfully"
+}
+```
+
+**Error Responses:**
+- 400: No file path provided
+- 403: Invalid file path (security violation)
+- 404: File not found
+- 500: Server error during deletion
+
+**Example:**
+```javascript
+await fetch(`/api/attachments/delete?path=${encodeURIComponent(filePath)}`, {
+  method: 'DELETE',
+  credentials: 'include'
+});
+```
+
+**Note:** When deleting a fuel record, service record, or recurring expense, the associated attachment is automatically deleted.
+
+---
+
 ## Data Models
 
 ### FuelRecord