fix: move resetPassword email locales to server i18n

The password reset email is rendered server-side via emaili18n.js,
which loads translations from server/i18n. The email.resetPassword
keys only existed in the frontend src/i18n locales, so t() returned
the raw key paths in the sent email. Move the EN/DE block to the
server locales and drop the unused copy from the frontend.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/i18n/en.json

@@ -11,6 +11,13 @@
       "validity": "This link is valid for 24 hours.",
       "footer": "If you didn't register, please ignore this email."
     },
+    "resetPassword": {
+      "subject": "{appName} - Reset your password",
+      "intro": "You requested to reset your password. Click the button below to set a new one:",
+      "button": "Reset Password",
+      "validity": "This link is valid for 1 hour.",
+      "footer": "If you didn't request this, you can safely ignore this email — your password will remain unchanged."
+    },
     "invite": {
       "subject": "{appName} - You've been invited",
       "title": "You have been invited",