feat: add report_date to monitoring sessions and update related functionality

fix: chart properly renders centered

backend/migrate_add_session_report_date.py

@@ -0,0 +1,41 @@
+"""
+Migration: add report_date to monitoring_sessions.
+
+Run once:
+    python backend/migrate_add_session_report_date.py
+
+Or inside the container:
+    docker exec terra-view-terra-view-1 python3 backend/migrate_add_session_report_date.py
+"""
+
+import sys
+import os
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from backend.database import engine
+from sqlalchemy import text
+
+def run():
+    with engine.connect() as conn:
+        # Check which columns already exist
+        result = conn.execute(text("PRAGMA table_info(monitoring_sessions)"))
+        existing = {row[1] for row in result}
+
+        added = []
+        for col, definition in [
+            ("report_date", "DATE"),
+        ]:
+            if col not in existing:
+                conn.execute(text(f"ALTER TABLE monitoring_sessions ADD COLUMN {col} {definition}"))
+                added.append(col)
+            else:
+                print(f"  Column '{col}' already exists — skipping.")
+
+        conn.commit()
+
+        if added:
+            print(f"  Added columns: {', '.join(added)}")
+        print("Migration complete.")
+
+if __name__ == "__main__":
+    run()