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/background/scheduler.py

@@ -0,0 +1,127 @@
+from apscheduler.schedulers.asyncio import AsyncIOScheduler
+from apscheduler.triggers.cron import CronTrigger
+from loguru import logger
+
+from leggend.config import config
+from leggend.services.sync_service import SyncService
+
+
+class BackgroundScheduler:
+    def __init__(self):
+        self.scheduler = AsyncIOScheduler()
+        self.sync_service = SyncService()
+
+    def start(self):
+        """Start the scheduler and configure sync jobs based on configuration"""
+        schedule_config = config.scheduler_config.get("sync", {})
+        
+        if not schedule_config.get("enabled", True):
+            logger.info("Sync scheduling is disabled in configuration")
+            self.scheduler.start()
+            return
+
+        # Use custom cron expression if provided, otherwise use hour/minute
+        if schedule_config.get("cron"):
+            # Parse custom cron expression (e.g., "0 3 * * *" for daily at 3 AM)
+            try:
+                cron_parts = schedule_config["cron"].split()
+                if len(cron_parts) == 5:
+                    minute, hour, day, month, day_of_week = cron_parts
+                    trigger = CronTrigger(
+                        minute=minute,
+                        hour=hour,
+                        day=day if day != "*" else None,
+                        month=month if month != "*" else None,
+                        day_of_week=day_of_week if day_of_week != "*" else None,
+                    )
+                else:
+                    logger.error(f"Invalid cron expression: {schedule_config['cron']}")
+                    return
+            except Exception as e:
+                logger.error(f"Error parsing cron expression: {e}")
+                return
+        else:
+            # Use hour/minute configuration (default: 3:00 AM daily)
+            hour = schedule_config.get("hour", 3)
+            minute = schedule_config.get("minute", 0)
+            trigger = CronTrigger(hour=hour, minute=minute)
+
+        self.scheduler.add_job(
+            self._run_sync,
+            trigger,
+            id="daily_sync",
+            name="Scheduled sync of all transactions",
+            max_instances=1,
+        )
+        
+        self.scheduler.start()
+        logger.info(f"Background scheduler started with sync job: {trigger}")
+
+    def shutdown(self):
+        if self.scheduler.running:
+            self.scheduler.shutdown()
+            logger.info("Background scheduler shutdown")
+
+    def reschedule_sync(self, schedule_config: dict):
+        """Reschedule the sync job with new configuration"""
+        if self.scheduler.running:
+            try:
+                self.scheduler.remove_job("daily_sync")
+                logger.info("Removed existing sync job")
+            except Exception:
+                pass  # Job might not exist
+
+            if not schedule_config.get("enabled", True):
+                logger.info("Sync scheduling disabled")
+                return
+
+            # Configure new schedule
+            if schedule_config.get("cron"):
+                try:
+                    cron_parts = schedule_config["cron"].split()
+                    if len(cron_parts) == 5:
+                        minute, hour, day, month, day_of_week = cron_parts
+                        trigger = CronTrigger(
+                            minute=minute,
+                            hour=hour,
+                            day=day if day != "*" else None,
+                            month=month if month != "*" else None,
+                            day_of_week=day_of_week if day_of_week != "*" else None,
+                        )
+                    else:
+                        logger.error(f"Invalid cron expression: {schedule_config['cron']}")
+                        return
+                except Exception as e:
+                    logger.error(f"Error parsing cron expression: {e}")
+                    return
+            else:
+                hour = schedule_config.get("hour", 3)
+                minute = schedule_config.get("minute", 0)
+                trigger = CronTrigger(hour=hour, minute=minute)
+
+            self.scheduler.add_job(
+                self._run_sync,
+                trigger,
+                id="daily_sync",
+                name="Scheduled sync of all transactions",
+                max_instances=1,
+            )
+            logger.info(f"Rescheduled sync job with: {trigger}")
+
+    async def _run_sync(self):
+        try:
+            logger.info("Starting scheduled sync job")
+            await self.sync_service.sync_all_accounts()
+            logger.info("Scheduled sync job completed successfully")
+        except Exception as e:
+            logger.error(f"Scheduled sync job failed: {e}")
+
+    def get_next_sync_time(self):
+        """Get the next scheduled sync time"""
+        job = self.scheduler.get_job("daily_sync")
+        if job:
+            return job.next_run_time
+        return None
+
+
+scheduler = BackgroundScheduler()