fix: prevent process.exit(1) on single user API failure (#61)

[rishab11250]

Description

Prevents process.exit(1) when a single user's LeetCode API call fails. Previously, one transient API failure would kill the entire sync cycle — losing all previously fetched data for other users. Now, failed users are logged and skipped, and syncing continues for the remaining users.

Additionally adds a 15-second axios timeout (default is 0 = infinite) to prevent a hanging request from silently destroying the entire 6-hour CI run.

Linked Issue

Fixes #61

Changes Made

• Added { timeout: 15000 } to axios.get() call — prevents infinite hangs on unresponsive API
• Changed process.exit(1) to return null on API failure — keeps the process alive
• Improved error message to include the failing URL — easier debugging
• Added null check in the user loop with continue — skips failed users gracefully

Type of Change

• Bug fix
• New feature
• UI/Visual update
• Documentation update
• Refactor

Testing

• Tested locally
• Tested on mobile viewport (if applicable)
• No console errors introduced

Verification performed:

• node --check scripts/sync-leaderboard.js — Syntax OK
• npx prettier --check "frontend/**/*.{html,css,js}" "scripts/**/*.js" "server.js" — All files pass

Checklist

• My code follows the project's coding style
• I have formatted my code locally using Prettier
• I have performed a self-review of my code
• My changes generate no new warnings or errors
• I have updated documentation if required
• I have linked the relevant issue

Screenshots / Screen Recording

N/A — Backend-only change with no UI impact.

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