refactor: move language selector into tenant email fieldset

Improved UI organization by moving the language selector into the same fieldset
as the tenant email input, since both are related to email notifications. The
language selector now only appears when email notifications are enabled.

Changes:
- Move language selector inside tenant email fieldset (no separate fieldset)
- Add label for tenant email input field
- Simplify notification language label text
- Remove unused notification-language-legend translation key
- Language selector shares visibility condition with email field

This provides a more logical grouping of related settings and reduces visual
clutter when email notifications are disabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web-app/messages/hr.json

@@ -194,6 +194,7 @@
     "rent-amount-label": "Iznos najamnine",
     "rent-amount-placeholder": "unesite iznos najamnine",
     "tenant-email-legend": "EMAIL PODSTANARA",
+    "tenant-email-label": "Obavijesti podstanara šalji na e-mail adresu:",
     "tenant-email-placeholder": "unesite email podstanara",
     "email-status": {
       "reset-button-label": "Reset",
@@ -204,8 +205,7 @@
       "verified": "podstanar je potvrdio ovu e-mail adresu",
       "unsubscribed": "podstanar je odjavio ovu e-mail adresu"
     },
-    "notification-language-legend": "JEZIK ZA OBAVIJESTI",
-    "notification-language-label": "Jezik za automatske obavijesti putem e-maila",
+    "notification-language-label": "Obavijesti za podstanara šalji na jeziku:",
     "notification-language-option-hr": "Hrvatski",
     "notification-language-option-en": "Engleski (English)",
     "warning-missing-tenant-names": "Upozorenje: Ime i prezime podstanara nedostaju. 2D barkod neće biti prikazan podstanaru kada otvori podijeljenu poveznicu dok oba polja ne budu popunjena.",