[QA] Non-existent pages return HTTP 200 instead of 404 (SPA catch-all)

[jarvisstark011010-cpu]

Steps to Reproduce

1. Navigate to https://smshub.dev/this-page-does-not-exist-xyz123
2. Check HTTP status code in DevTools → Network tab

Expected

HTTP 404 status code with user-friendly error page and link back to home

Actual

HTTP 200 returned. No 404 message shown to user.

Root Cause

SPA client-side router serves index.html for all routes. Server should return 404 for truly non-existent paths.

Severity

Medium

Impact

• SEO: Search engines index invalid URLs as valid pages
• Monitoring: Cannot detect broken links (always 200)
• UX: Users not informed the page doesn't exist