Remove Discord and Google OAuth verification from CMS

- Remove Discord + Google OAuth providers from NextAuth config
- Remove social login buttons (Discord/Google) from login form
- Delete link-discord.ts action and discord-verify-form.tsx component
- Simplify verify page to email-only verification flow
- Remove connections settings page and its link from settings
- Clean env.ts, .env, .env.example of Discord/Google client vars
- Remove discordUrl social icon from register, login, and homepage
- Clean translation files: remove continueWithDiscord, continueWithGoogle, connections keys

.env.example

@@ -47,12 +47,6 @@ RCON_PORT=3001
 # Falls back to NEXT_PUBLIC_APP_URL/imaging when only the app URL is set.
 # NEXT_PUBLIC_IMAGER_URL=https://epicnabbo.nl/imaging
 
-# Optional OAuth (enabled when both id+secret are set)
-DISCORD_CLIENT_ID=
-DISCORD_CLIENT_SECRET=
-GOOGLE_CLIENT_ID=
-GOOGLE_CLIENT_SECRET=
-
 # Preferred email provider (HTTP API). Used before SMTP when set.
 RESEND_API_KEY=