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/sync.py

@@ -0,0 +1,55 @@
+from datetime import datetime
+from typing import Optional, Dict, Any
+
+from pydantic import BaseModel
+
+
+class SyncRequest(BaseModel):
+    """Request to trigger a sync"""
+    account_ids: Optional[list[str]] = None  # If None, sync all accounts
+    force: bool = False  # Force sync even if recently synced
+
+
+class SyncStatus(BaseModel):
+    """Sync operation status"""
+    is_running: bool
+    last_sync: Optional[datetime] = None
+    next_sync: Optional[datetime] = None
+    accounts_synced: int = 0
+    total_accounts: int = 0
+    transactions_added: int = 0
+    errors: list[str] = []
+    
+    class Config:
+        json_encoders = {
+            datetime: lambda v: v.isoformat() if v else None
+        }
+
+
+class SyncResult(BaseModel):
+    """Result of a sync operation"""
+    success: bool
+    accounts_processed: int
+    transactions_added: int
+    transactions_updated: int
+    balances_updated: int
+    duration_seconds: float
+    errors: list[str] = []
+    started_at: datetime
+    completed_at: datetime
+    
+    class Config:
+        json_encoders = {
+            datetime: lambda v: v.isoformat()
+        }
+
+
+class SchedulerConfig(BaseModel):
+    """Scheduler configuration model"""
+    enabled: bool = True
+    hour: Optional[int] = 3
+    minute: Optional[int] = 0
+    cron: Optional[str] = None  # Custom cron expression
+    
+    class Config:
+        extra = "forbid"