Add automatic schema versioning with startup migration

On startup, the app now checks if the database schema version matches
the code. If there's a mismatch or no version exists, it automatically
runs a full data migration before starting.

- Add backend/version.py with SCHEMA_VERSION constant
- Add backend/migration.py with extracted migration logic
- Add SchemaVersion model to track DB version
- Add version check functions to database.py
- Update app.py lifespan to use check_and_migrate_if_needed()
- Simplify migrate_csv_to_db.py to use shared logic

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/database.py

@@ -2,7 +2,10 @@
 Database connection setup using SQLAlchemy.
 """
 
-from sqlalchemy import create_engine
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import create_engine, inspect
 from sqlalchemy.orm import sessionmaker, declarative_base
 from contextlib import contextmanager
 
@@ -65,3 +68,80 @@ def drop_db():
     """
     Base.metadata.drop_all(bind=engine)
 
+
+def get_db_schema_version() -> Optional[int]:
+    """
+    Get the current schema version from the database.
+    Returns None if table doesn't exist or no version is set.
+    """
+    from .models import SchemaVersion  # Import here to avoid circular imports
+
+    # Check if schema_version table exists
+    inspector = inspect(engine)
+    if "schema_version" not in inspector.get_table_names():
+        return None
+
+    try:
+        with get_db_session() as db:
+            row = db.query(SchemaVersion).first()
+            return row.version if row else None
+    except Exception:
+        return None
+
+
+def set_db_schema_version(version: int):
+    """
+    Set/update the schema version in the database.
+    Creates the row if it doesn't exist.
+    """
+    from .models import SchemaVersion
+
+    with get_db_session() as db:
+        row = db.query(SchemaVersion).first()
+        if row:
+            row.version = version
+            row.migrated_at = datetime.utcnow()
+        else:
+            db.add(SchemaVersion(id=1, version=version, migrated_at=datetime.utcnow()))
+
+
+def check_and_migrate_if_needed():
+    """
+    Check schema version and run migration if needed.
+    Called during application startup.
+    """
+    from .version import SCHEMA_VERSION
+    from .migration import run_full_migration
+
+    db_version = get_db_schema_version()
+
+    if db_version == SCHEMA_VERSION:
+        print(f"Schema version {SCHEMA_VERSION} matches. Fast startup.")
+        # Still ensure tables exist (they should if version matches)
+        init_db()
+        return
+
+    if db_version is None:
+        print(f"No schema version found. Running initial migration (v{SCHEMA_VERSION})...")
+    else:
+        print(f"Schema mismatch: DB has v{db_version}, code expects v{SCHEMA_VERSION}")
+        print("Running full migration...")
+
+    try:
+        success = run_full_migration(geocode=False)
+
+        if success:
+            # Ensure schema_version table exists before writing
+            init_db()
+            set_db_schema_version(SCHEMA_VERSION)
+            print(f"Migration complete. Schema version set to {SCHEMA_VERSION}")
+        else:
+            print("Warning: Migration completed but no data was imported.")
+            init_db()
+            set_db_schema_version(SCHEMA_VERSION)
+
+    except Exception as e:
+        print(f"FATAL: Migration failed: {e}")
+        print("Application cannot start. Please check database and CSV files.")
+        raise
+