unit history added

backend/models.py

@@ -59,6 +59,24 @@ class IgnoredUnit(Base):
     ignored_at = Column(DateTime, default=datetime.utcnow)
 
 
+class UnitHistory(Base):
+    """
+    Unit history: complete timeline of changes to each unit.
+    Tracks note changes, status changes, deployment/benched events, and more.
+    """
+    __tablename__ = "unit_history"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    unit_id = Column(String, nullable=False, index=True)  # FK to RosterUnit.id
+    change_type = Column(String, nullable=False)  # note_change, deployed_change, retired_change, etc.
+    field_name = Column(String, nullable=True)  # Which field changed
+    old_value = Column(Text, nullable=True)  # Previous value
+    new_value = Column(Text, nullable=True)  # New value
+    changed_at = Column(DateTime, default=datetime.utcnow, nullable=False, index=True)
+    source = Column(String, default="manual")  # manual, csv_import, telemetry, offline_sync
+    notes = Column(Text, nullable=True)  # Optional reason/context for the change
+
+
 class UserPreferences(Base):
     """
     User preferences: persistent storage for application settings.