fix(security): validate redirect_uri to prevent open redirect attacks

[lakhansamani]

Summary

• Added isValidRedirectUri() validation in AuthorizerResetPassword.svelte — redirect_uri is now validated against same-origin and configured redirect URL before use
• Prevents attacker-controlled redirect_uri from redirecting users to malicious sites after password reset

Companion PRs

• fix(security): validate redirect_uri to prevent open redirect attacks authorizer#579 (main login app fix)
• fix(security): validate redirect_uri to prevent open redirect attacks authorizer-react#52 (React SDK fix)

Test plan

• Verify password reset redirects work for same-origin URLs
• Verify cross-origin redirect to evil.com is blocked
• Verify configured redirect_uri still works