feat: add database models and alembic setup

- SQLAlchemy async models for sources, jobs, schedules, executions, backups, settings
- Alembic migration configuration

backend/app/database.py

@@ -0,0 +1,16 @@
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
+from sqlalchemy.orm import declarative_base
+
+DATABASE_URL = "sqlite+aiosqlite:///./backup_tool.db"
+
+engine = create_async_engine(DATABASE_URL, echo=True)
+AsyncSessionLocal = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)
+
+Base = declarative_base()
+
+async def get_db():
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+        finally:
+            await session.close()

backend/app/models.py

@@ -0,0 +1,82 @@
+from sqlalchemy import Column, Integer, String, DateTime, Boolean, Text, ForeignKey, JSON
+from sqlalchemy.orm import relationship
+from datetime import datetime
+from .database import Base
+
+class Source(Base):
+    __tablename__ = "sources"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String, nullable=False)
+    type = Column(String, nullable=False)  # local, ssh, database
+    config = Column(JSON, default=dict)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    
+    jobs = relationship("Job", back_populates="source", cascade="all, delete-orphan")
+
+class Job(Base):
+    __tablename__ = "jobs"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String, nullable=False)
+    source_id = Column(Integer, ForeignKey("sources.id"), nullable=False)
+    strategy = Column(String, nullable=False, default="full")  # full, incremental
+    destination_path = Column(String, nullable=False)
+    exclude_patterns = Column(JSON, default=list)
+    enabled = Column(Boolean, default=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    
+    source = relationship("Source", back_populates="jobs")
+    schedule = relationship("Schedule", back_populates="job", uselist=False, cascade="all, delete-orphan")
+    executions = relationship("JobExecution", back_populates="job", cascade="all, delete-orphan")
+
+class Schedule(Base):
+    __tablename__ = "schedules"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    job_id = Column(Integer, ForeignKey("jobs.id"), unique=True, nullable=False)
+    cron_expression = Column(String, nullable=False)
+    enabled = Column(Boolean, default=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    
+    job = relationship("Job", back_populates="schedule")
+
+class JobExecution(Base):
+    __tablename__ = "job_executions"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    job_id = Column(Integer, ForeignKey("jobs.id"), nullable=False)
+    status = Column(String, nullable=False, default="pending")  # pending, running, success, failed, cancelled
+    started_at = Column(DateTime, nullable=True)
+    completed_at = Column(DateTime, nullable=True)
+    bytes_processed = Column(Integer, default=0)
+    bytes_backed_up = Column(Integer, default=0)
+    error_message = Column(Text, nullable=True)
+    triggered_by = Column(String, nullable=False)  # manual, schedule
+    
+    job = relationship("Job", back_populates="executions")
+    backups = relationship("Backup", back_populates="execution", cascade="all, delete-orphan")
+
+class Backup(Base):
+    __tablename__ = "backups"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    execution_id = Column(Integer, ForeignKey("job_executions.id"), nullable=False)
+    storage_path = Column(String, nullable=False)
+    size_bytes = Column(Integer, default=0)
+    checksum = Column(String, nullable=True)
+    type = Column(String, nullable=False)  # full, incremental
+    parent_backup_id = Column(Integer, ForeignKey("backups.id"), nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    
+    execution = relationship("JobExecution", back_populates="backups")
+    parent_backup = relationship("Backup", remote_side=[id])
+
+class Setting(Base):
+    __tablename__ = "settings"
+    
+    key = Column(String, primary_key=True)
+    value = Column(Text, nullable=True)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)