feat: implement caching for google sheets data

- Add cache_utils.py with JSON caching for Google Sheets
- Authenticate and cache Drive/Sheets API services globally to reuse tokens
- Use CACHE_SHEET_MAP dict to resolve cache names securely to Sheet IDs
- Change app.py data fetching to skip downloads if modifiedTime matches cache
- Replace global socket timeout with httplib2 to fix Werkzeug timeouts
- Add VS Code attach debugpy configurations to launch.json and Makefile

scripts/match_payments.py

@@ -300,8 +300,8 @@ def reconcile(
             norm_name = normalize(name)
             norm_period = normalize(m)
             fee_data = member_fees[name].get(m, (0, 0))
-            original_expected = fee_data[0] if isinstance(fee_data, tuple) else fee_data
-            attendance_count = fee_data[1] if isinstance(fee_data, tuple) else 0
+            original_expected = fee_data[0] if isinstance(fee_data, (tuple, list)) else fee_data
+            attendance_count = fee_data[1] if isinstance(fee_data, (tuple, list)) else 0
             
             ex_data = exceptions.get((norm_name, norm_period))
             if ex_data is not None: