feat: Transform to web architecture with FastAPI backend

This major update transforms leggen from CLI-only to a web-ready
architecture while maintaining full CLI compatibility.

New Features:
- FastAPI backend service (leggend) with comprehensive REST API
- Background job scheduler with configurable cron (replaces Ofelia)
- All CLI commands refactored to use API endpoints
- Docker configuration updated for new services
- API client with health checks and error handling

API Endpoints:
- /api/v1/banks/* - Bank connections and institutions
- /api/v1/accounts/* - Account management and balances
- /api/v1/transactions/* - Transaction retrieval with filtering
- /api/v1/sync/* - Manual sync and scheduler configuration
- /api/v1/notifications/* - Notification settings management

CLI Enhancements:
- New --api-url option and LEGGEND_API_URL environment variable
- Enhanced sync command with --wait and --force options
- Improved transactions command with --full and --limit options
- Automatic fallback and health checking

Breaking Changes:
- compose.yml structure updated (leggend service added)
- Ofelia scheduler removed (internal scheduler used instead)

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

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

leggend/api/models/accounts.py

@@ -0,0 +1,70 @@
+from datetime import datetime
+from typing import List, Optional, Dict, Any
+
+from pydantic import BaseModel
+
+
+class AccountBalance(BaseModel):
+    """Account balance model"""
+    amount: float
+    currency: str
+    balance_type: str
+    last_change_date: Optional[datetime] = None
+    
+    class Config:
+        json_encoders = {
+            datetime: lambda v: v.isoformat() if v else None
+        }
+
+
+class AccountDetails(BaseModel):
+    """Account details model"""
+    id: str
+    institution_id: str
+    status: str
+    iban: Optional[str] = None
+    name: Optional[str] = None
+    currency: Optional[str] = None
+    created: datetime
+    last_accessed: Optional[datetime] = None
+    balances: List[AccountBalance] = []
+    
+    class Config:
+        json_encoders = {
+            datetime: lambda v: v.isoformat() if v else None
+        }
+
+
+class Transaction(BaseModel):
+    """Transaction model"""
+    internal_transaction_id: str
+    institution_id: str
+    iban: Optional[str] = None
+    account_id: str
+    transaction_date: datetime
+    description: str
+    transaction_value: float
+    transaction_currency: str
+    transaction_status: str  # "booked" or "pending"
+    raw_transaction: Dict[str, Any]
+    
+    class Config:
+        json_encoders = {
+            datetime: lambda v: v.isoformat()
+        }
+
+
+class TransactionSummary(BaseModel):
+    """Transaction summary for lists"""
+    internal_transaction_id: str
+    date: datetime
+    description: str
+    amount: float
+    currency: str
+    status: str
+    account_id: str
+    
+    class Config:
+        json_encoders = {
+            datetime: lambda v: v.isoformat()
+        }