refactor: Unify leggen and leggend packages into single leggen package

- Merge leggend API components into leggen (api/, services/, background/)
- Replace leggend command with 'leggen server' subcommand
- Consolidate configuration systems into leggen.utils.config
- Update environment variables: LEGGEND_API_URL -> LEGGEN_API_URL
- Rename LeggendAPIClient -> LeggenAPIClient
- Update all documentation, Docker configs, and compose files
- Fix all import statements and test references
- Remove duplicate utility files and clean up package structure

All tests passing (101/101), linting clean, server functionality preserved.

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

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

leggen/utils/config.py

@@ -1,9 +1,146 @@
+import os
 import sys
 import tomllib
+import tomli_w
+from pathlib import Path
+from typing import Dict, Any, Optional
 
 import click
+from loguru import logger
 
 from leggen.utils.text import error
+from leggen.utils.paths import path_manager
+
+
+class Config:
+    _instance = None
+    _config = None
+    _config_path = None
+
+    def __new__(cls):
+        if cls._instance is None:
+            cls._instance = super().__new__(cls)
+        return cls._instance
+
+    def load_config(self, config_path: Optional[str] = None) -> Dict[str, Any]:
+        if self._config is not None:
+            return self._config
+
+        if config_path is None:
+            config_path = os.environ.get("LEGGEN_CONFIG_FILE")
+            if not config_path:
+                config_path = str(path_manager.get_config_file_path())
+
+        self._config_path = config_path
+
+        try:
+            with open(config_path, "rb") as f:
+                self._config = tomllib.load(f)
+                logger.info(f"Configuration loaded from {config_path}")
+        except FileNotFoundError:
+            logger.error(f"Configuration file not found: {config_path}")
+            raise
+        except Exception as e:
+            logger.error(f"Error loading configuration: {e}")
+            raise
+
+        return self._config
+
+    def save_config(
+        self,
+        config_data: Optional[Dict[str, Any]] = None,
+        config_path: Optional[str] = None,
+    ) -> None:
+        """Save configuration to TOML file"""
+        if config_data is None:
+            config_data = self._config
+
+        if config_path is None:
+            config_path = self._config_path or os.environ.get("LEGGEN_CONFIG_FILE")
+            if not config_path:
+                config_path = str(path_manager.get_config_file_path())
+
+        if config_path is None:
+            raise ValueError("No config path specified")
+        if config_data is None:
+            raise ValueError("No config data to save")
+
+        # Ensure directory exists
+        Path(config_path).parent.mkdir(parents=True, exist_ok=True)
+
+        try:
+            with open(config_path, "wb") as f:
+                tomli_w.dump(config_data, f)
+
+            # Update in-memory config
+            self._config = config_data
+            self._config_path = config_path
+            logger.info(f"Configuration saved to {config_path}")
+        except Exception as e:
+            logger.error(f"Error saving configuration: {e}")
+            raise
+
+    def update_config(self, section: str, key: str, value: Any) -> None:
+        """Update a specific configuration value"""
+        if self._config is None:
+            self.load_config()
+
+        if self._config is None:
+            raise RuntimeError("Failed to load config")
+
+        if section not in self._config:
+            self._config[section] = {}
+
+        self._config[section][key] = value
+        self.save_config()
+
+    def update_section(self, section: str, data: Dict[str, Any]) -> None:
+        """Update an entire configuration section"""
+        if self._config is None:
+            self.load_config()
+
+        if self._config is None:
+            raise RuntimeError("Failed to load config")
+
+        self._config[section] = data
+        self.save_config()
+
+    @property
+    def config(self) -> Dict[str, Any]:
+        if self._config is None:
+            self.load_config()
+        if self._config is None:
+            raise RuntimeError("Failed to load config")
+        return self._config
+
+    @property
+    def gocardless_config(self) -> Dict[str, str]:
+        return self.config.get("gocardless", {})
+
+    @property
+    def database_config(self) -> Dict[str, Any]:
+        return self.config.get("database", {})
+
+    @property
+    def notifications_config(self) -> Dict[str, Any]:
+        return self.config.get("notifications", {})
+
+    @property
+    def filters_config(self) -> Dict[str, Any]:
+        return self.config.get("filters", {})
+
+    @property
+    def scheduler_config(self) -> Dict[str, Any]:
+        """Get scheduler configuration with defaults"""
+        default_schedule = {
+            "sync": {
+                "enabled": True,
+                "hour": 3,
+                "minute": 0,
+                "cron": None,  # Optional custom cron expression
+            }
+        }
+        return self.config.get("scheduler", default_schedule)
 
 
 def load_config(ctx: click.Context, _, filename):
@@ -16,3 +153,7 @@ def load_config(ctx: click.Context, _, filename):
             "Configuration file not found. Provide a valid configuration file path with leggen --config <path> or LEGGEN_CONFIG=<path> environment variable."
         )
         sys.exit(1)
+
+
+# Global singleton instance
+config = Config()