[Enhancement] Add password visibility toggle on login and signup

[niat-web]

Feature Request

Current behavior:
Password field always shows dots (hidden).
User cannot verify what they are typing.

Expected behavior:
Add an eye icon inside the password field.

• Click eye icon → show password as plain text
• Click again → hide password (dots)

Why this is important:
Users often make typos in password fields.
Being able to see what you typed
reduces login failures and frustration.

Technical implementation:

• Add state: showPassword (true/false)
• Toggle input type between "password" and "text"
• Add eye/eye-off icon button inside input field
• Apply to: LoginPage, RegisterPage

Acceptance Criteria:

• Eye icon visible in password field on login page
• Eye icon visible in password field on signup page
• Eye icon visible in confirm password field on signup
• Clicking toggles password visibility