chore: remove obsolete .env.example and add issue #98 reference

- Remove .env.example to prevent configuration confusion
- furt now uses only furt.conf for all configuration
- .env.example was misleading users during installation
- Add comment referencing issue #98 resolution

Eliminates config method ambiguity identified in installation testing.
Closes DAW/furt#98

.env.example

@@ -1,41 +0,0 @@
-# Gitea-Konfiguration für Issue-Management
-GITEA_URL=https://your-gitea-instance.com
-REPO_OWNER=your-username
-REPO_NAME=furt
-GITEA_TOKEN=your-gitea-token-here
-
-# Optional: Default-Assignee für Issues
-DEFAULT_ASSIGNEE=your-username
-
-# Lua-Konfiguration
-LUA_COMMAND=lua51
-LUA_VERSION=5.1
-
-# Gateway-Konfiguration (für Entwicklung)
-GATEWAY_PORT=8080
-GATEWAY_LOG_LEVEL=info
-
-# CORS-Konfiguration (comma-separated list)
-# Development (default if not set):
-# CORS_ALLOWED_ORIGINS=http://localhost:1313,http://127.0.0.1:1313
-#
-# Production example:
-# CORS_ALLOWED_ORIGINS=https://yourdomain.com,https://www.yourdomain.com
-CORS_ALLOWED_ORIGINS=http://localhost:1313,http://127.0.0.1:1313
-
-# Service-Ports (für lokale Entwicklung)
-FORMULAR2MAIL_PORT=8081
-SAGJAN_PORT=8082
-
-# SMTP-Konfiguration (für formular2mail)
-SMTP_HOST=localhost
-SMTP_PORT=25
-SMTP_USERNAME=noreply@example.com
-SMTP_PASSWORD=secret-password
-SMTP_FROM=noreply@example.com
-SMTP_TO=admin@example.com
-
-# API-Schlüssel (generiere sichere Schlüssel für Produktion!)
-HUGO_API_KEY=hugo-dev-key-change-in-production
-ADMIN_API_KEY=admin-dev-key-change-in-production
-