test: update test suite for OmegaConf config system

- Add tests/conftest.py with make_settings() helper that maps legacy config
  parameter names to new nested OmegaConf structure
- Update all test files to use the conftest fixture
- All 73 tests now pass with new config system
- Maintains backward compatibility via Settings class properties

Also add AGENTS.md with comprehensive AI agent guidelines:
- Project overview and key technologies
- Directory structure reference
- Development workflow and common tasks
- Testing strategy and patterns
- CI/CD pipeline overview
- Common pitfalls and best practices
- Debugging guide for agents working on the project

tests/conftest.py

@@ -0,0 +1,91 @@
+"""Shared test fixtures and utilities."""
+
+from steward.config import (
+    AnalysisConfig,
+    MemoryConfig,
+    OpenAIConfig,
+    Settings,
+    TelegramConfig,
+    ToolsConfig,
+)
+
+
+def make_settings(**kwargs) -> Settings:
+    """Create a Settings instance from old-style kwargs.
+
+    Maps legacy parameter names to the new nested structure:
+    - telegram_bot_token -> telegram.bot_token
+    - telegram_allowed_user_ids -> telegram.allowed_user_ids
+    - telegram_group_ids -> telegram.group_ids
+    - openai_api_key -> openai.api_key
+    - openai_base_url -> openai.base_url
+    - openai_model -> openai.model
+    - openai_system_prompt -> openai.system_prompt
+    - analysis_target_url -> analysis.target_url
+    - analysis_target_api_key -> analysis.target_api_key
+    - analysis_cron_hour -> analysis.cron_hour
+    - analysis_cron_minute -> analysis.cron_minute
+    - thread_memory_path -> memory.thread_memory_path
+    - mcp_server_url -> tools.mcp_server_url
+    - mcp_server_api_key -> tools.mcp_server_api_key
+
+    Args:
+        **kwargs: Legacy-style configuration parameters
+
+    Returns:
+        Settings: A fully constructed Settings instance
+    """
+    # Extract telegram config
+    telegram_config = TelegramConfig(
+        bot_token=kwargs.pop("telegram_bot_token", ""),
+        allowed_user_ids=kwargs.pop("telegram_allowed_user_ids", []),
+        group_ids=kwargs.pop("telegram_group_ids", []),
+    )
+
+    # Extract OpenAI config
+    openai_config = OpenAIConfig(
+        api_key=kwargs.pop("openai_api_key", ""),
+        base_url=kwargs.pop("openai_base_url", "https://api.openai.com/v1"),
+        model=kwargs.pop("openai_model", "gpt-4o"),
+        system_prompt=kwargs.pop(
+            "openai_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."
+            ),
+        ),
+    )
+
+    # Extract analysis config
+    analysis_config = AnalysisConfig(
+        target_url=kwargs.pop("analysis_target_url", ""),
+        target_api_key=kwargs.pop("analysis_target_api_key", ""),
+        cron_hour=kwargs.pop("analysis_cron_hour", 8),
+        cron_minute=kwargs.pop("analysis_cron_minute", 0),
+    )
+
+    # Extract memory config
+    memory_config = MemoryConfig(
+        thread_memory_path=kwargs.pop("thread_memory_path", "thread_memory.json"),
+    )
+
+    # Extract tools config
+    tools_config = ToolsConfig(
+        mcp_server_url=kwargs.pop("mcp_server_url", ""),
+        mcp_server_api_key=kwargs.pop("mcp_server_api_key", ""),
+    )
+
+    # Any remaining kwargs should be rejected
+    if kwargs:
+        raise TypeError(f"Unexpected keyword arguments: {', '.join(kwargs.keys())}")
+
+    # Create and return Settings instance
+    return Settings(
+        telegram=telegram_config,
+        openai=openai_config,
+        analysis=analysis_config,
+        memory=memory_config,
+        tools=tools_config,
+    )