chore: add example.env configuration file

- Added example.env file with environment variable template
- Replaces the removed env.example file with updated format

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

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

example.env

@@ -0,0 +1,23 @@
+# Database
+POSTGRES_URL=postgresql://dev_user:dev_password@localhost:5432/agentic_coding_dev
+
+# Authentication - Better Auth
+# Generate key using https://www.better-auth.com/docs/installation
+BETTER_AUTH_SECRET=qtD4Ssa0t5jY7ewALgai97sKhAtn7Ysc
+
+# Google OAuth (Get from Google Cloud Console)
+GOOGLE_CLIENT_ID=
+GOOGLE_CLIENT_SECRET=
+
+# AI Integration (Optional - for chat functionality)
+OPENAI_API_KEY=
+OPENAI_MODEL="gpt-5-mini"
+
+# Optional - for vector search only
+OPENAI_EMBEDDING_MODEL="text-embedding-3-large"
+
+# App URL (for production deployments)
+NEXT_PUBLIC_APP_URL="http://localhost:3000"
+
+# File storage (optional - if app required file uploads)
+BLOB_READ_WRITE_TOKEN=