URL encode base64 next parameter before htmlspecialchars in login form

[coderabbitai]

Description

When embedding the base64-encoded $_GET['next'] parameter in the login form action attribute in front/index.php, the + character from base64 encoding can be misinterpreted as a space during URL parsing.

Suggested Fix

Apply urlencode() before htmlspecialchars() when building the form action:

?next=' . htmlspecialchars(urlencode($_GET['next']), ENT_QUOTES, 'UTF-8')

This ensures the base64 value survives the round-trip through query string parsing.

Context

• File: front/index.php (form action around line 193)
• Original PR: Next release - deep link support after log in and refactor of index.php #1500
• Comment thread: Next release - deep link support after log in and refactor of index.php #1500 (comment)
• Requested by: @adamoutler

[adamoutler]

Not requested by me. Closing.