add password strength hints

[saurabhhhcodes]

What changed

• Added a shared password strength guide for the auth screens.
• Show real-time feedback for length, uppercase letters, numbers, and special characters.
• Added a live strength bar and per-rule checklist to login and signup password fields.
• Bumped signup password minimum length to 8 characters so the UI hint matches server validation.

Why

Users were only seeing a generic invalid-credentials error after submit, with no guidance on what the password needed.

Impact

People now get immediate feedback while typing, which makes signup clearer and reduces silent validation failures.

Validation

• git diff --check
• node --check server/src/services/userService.js
• npm run build in frontend

Closes #191

[vercel]

Someone is attempting to deploy a commit to the Sunil Kumar's projects Team on Vercel.

A member of the Team first needs to authorize it.