docs: rewrite README with structured overview and quick start guide

Replaces the minimal project description with a comprehensive README
including a component overview table, quick start instructions, common
Ansible operations, and links to detailed documentation. Aligns with
Red Panda Approval™ standards.

ansible/openwebui/openwebui.env.j2

@@ -0,0 +1,42 @@
+# OpenWebUI Environment Configuration
+
+# Server settings
+PORT={{openwebui_port}}
+HOST={{openwebui_host}}
+WEBUI_SECRET_KEY={{openwebui_secret_key}}
+CORS_ALLOW_ORIGIN={{openwebui_cors_allow_origin}}
+
+# Database configuration
+DATABASE_URL=postgresql://{{openwebui_db_user}}:{{openwebui_db_password}}@{{openwebui_db_host}}:{{openwebui_db_port}}/{{openwebui_db_name}}
+DATABASE_TYPE=postgres
+VECTOR_DB=pgvector
+PGVECTOR_CREATE_EXTENSION=false
+
+# Authentication settings
+ENABLE_SIGNUP={{openwebui_enable_signup}}
+ENABLE_EMAIL_LOGIN={{openwebui_enable_email_login}}
+
+# OAuth/OIDC Configuration (Casdoor SSO)
+ENABLE_OAUTH_SIGNUP=true
+OAUTH_CLIENT_ID={{openwebui_oauth_client_id}}
+OAUTH_CLIENT_SECRET={{openwebui_oauth_client_secret}}
+OAUTH_PROVIDER_NAME={{openwebui_oauth_provider_name}}
+OPENID_PROVIDER_URL={{openwebui_oauth_provider_url}}
+
+# API settings
+OPENAI_API_KEY={{openwebui_openai_api_key}}
+ANTHROPIC_API_KEY={{openwebui_anthropic_api_key}}
+MISTRAL_API_KEY={{openwebui_mistral_api_key}}
+GROQ_API_KEY={{openwebui_groq_api_key}}
+
+# Ollama LLM settings
+OLLAMA_API_BASE_URL={{ollama_api_base_url}}
+OLLAMA_API_KEY={{openwebui_ollama_api_key}}
+
+# Security settings
+ENABLE_HTTPS={{openwebui_enable_https}}
+SSL_CERT_PATH={{openwebui_ssl_cert_path}}
+SSL_KEY_PATH={{openwebui_ssl_key_path}}
+
+# Logging
+LOG_LEVEL={{openwebui_log_level}}