feat: implement OmegaConf-based configuration management with uv

Configuration changes:
- Replace pydantic-settings with OmegaConf for flexible config management
- Support YAML config files via CONFIG_FILE environment variable
- Support environment variables with STEWARD__SECTION__KEY format
- Add config_schema.yaml as default configuration schema
- Create pydantic models for each configuration section for type safety
- Maintain backward compatibility via properties on Settings class
- Add CONFIGURATION.md with comprehensive setup and usage guide
- Update pyproject.toml to include config_schema.yaml in package data

Build/deployment changes:
- Replace pip with uv in Dockerfile for faster dependency installation
- Create docker-compose.dev.yml for local development (build .)
- Keep docker-compose.yml for production (uses ghcr.io/djw4/steward:latest)
- Update .env.example with new STEWARD__* variable format

This setup is designed for Kubernetes deployment:
- Non-sensitive config goes in ConfigMap (config.yaml)
- Secrets go in Secret resources (environment variables)
- Single unified configuration system for all environments

steward/config_schema.yaml

@@ -0,0 +1,51 @@
+# Steward Configuration Schema
+# This is the default configuration. Override values in your own config file or via environment variables.
+# Environment variable format: STEWARD__<section>__<key>=value
+# Example: STEWARD__TELEGRAM__BOT_TOKEN=your_token
+
+telegram:
+  # Telegram bot token (REQUIRED - set via env or config)
+  bot_token: ""
+
+  # List of user IDs allowed to interact with the bot via DM
+  # Empty list means all users are allowed
+  allowed_user_ids: []
+
+  # List of group/channel IDs where the bot is allowed to operate
+  # Empty list means all groups are allowed
+  group_ids: []
+
+openai:
+  # OpenAI API key (REQUIRED - set via env for security)
+  api_key: ""
+
+  # API base URL (can use any OpenAI-compatible provider)
+  base_url: "https://api.openai.com/v1"
+
+  # Model to use
+  model: "gpt-4o"
+
+  # System prompt for the bot
+  system_prompt: "You are Steward, a persistent, trustworthy AI-assisted personal operations platform. You reduce cognitive load by observing, remembering, planning, and proposing actions. You are conservative, transparent, and policy-aware. Always explain your reasoning."
+
+analysis:
+  # Target URL for API analysis (optional - set to enable analysis feature)
+  target_url: ""
+
+  # API key for analysis target (optional)
+  target_api_key: ""
+
+  # Cron schedule for automatic analysis
+  cron_hour: 8
+  cron_minute: 0
+
+memory:
+  # Path to thread memory storage file
+  thread_memory_path: "thread_memory.json"
+
+tools:
+  # MCP/OpenAPI tool server URL (optional - set to enable tool calling)
+  mcp_server_url: ""
+
+  # API key for MCP server (optional)
+  mcp_server_api_key: ""