Login UI fixes: button size, placeholder, keyboard handling, and text update.

[clemPerrousset]

• Reduced "Je me connecte" button height to 48pt in OTLoginV2ViewController.
• Added .ignoresSafeArea(.keyboard) to LoginView (with iOS 14 fallback) to prevent the footer from moving up when the keyboard appears.
• Replaced hardcoded placeholder "Ex : 123456" with localized "Saisir votre code".
• Updated French localization for "Recevoir un nouveau code par sms" to "Redemander un code".
• Added login_code_placeholder key to all Localizable.strings files.

---

PR created automatically by Jules for task 8565434066970826646 started by @clemPerrousset

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.