fix: add missing answer notification enum type

[Anjali-collab21]

Description

Fixes #3
Fixes notification validation failure when creating answer notifications.

Problem

The backend creates notifications using:

type: 'answer'

inside server/routes/answers.js, but the Notification schema enum in server/models/Notification.js did not include "answer" as an allowed value.

This caused Mongoose validation to fail during notification creation while the answer itself was still created successfully.

Fix

Added "answer" to the allowed enum values in the Notification schema.

Verification

• Reproduced the issue locally
• Verified validation failure before the fix
• Confirmed successful notification creation after update
• Verified notifications are now stored correctly in MongoDB

[vercel]

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[Karanjot786]

Hey @Anjali-collab21! Saw your work on GSSoC 2026.

We are building TermUI, a TypeScript terminal UI framework with React-style hooks and JSX, rendered entirely in the terminal.

We have 67 unassigned GSSoC issues open. 19 are marked good first issue. Your JavaScript background transfers directly.

• Open issues (GSSoC 2026)
• TermUI on GSSoC

Karanjot, TermUI maintainer