Fix: commit missing init_db migration for sync_lookback_days column

This ALTER TABLE was written locally but never staged, so the production
image ran without it and the column was never added to the DB.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -40,6 +40,16 @@ async def init_db():
     except Exception as e:
         print(f"TimescaleDB hypertable skipped: {e}")
 
+    # Add columns that were introduced after initial table creation (non-fatal)
+    try:
+        async with engine.begin() as conn:
+            await conn.execute(text(
+                "ALTER TABLE garmin_connect_configs "
+                "ADD COLUMN IF NOT EXISTS sync_lookback_days INTEGER DEFAULT 30"
+            ))
+    except Exception as e:
+        print(f"Column migration skipped: {e}")
+
     # Seed admin user (only if password is configured)
     if not settings.admin_password:
         print("ADMIN_PASSWORD not set - skipping admin user seed")