fix: ensure plotly backend is set in result_view and custom routes

- Add pd.options.plotting.backend = 'plotly' at route level
- Fixes matplotlib ImportError in Railway deployment
- Ensures DataFrame.plot() uses plotly instead of matplotlib
- Resolves Internal Server Error on result_view pages

main.py

@@ -415,6 +415,10 @@ def custom_post():
     else:
         flash('使用投組功能請先登入。', 'warning')
         return redirect(url_for('login'))
+
+    # Ensure plotly backend is set
+    pd.options.plotting.backend = "plotly"
+
     port = pd.read_csv(request.files['csv_file'], index_col=0, parse_dates=True)
     role = request.form.get('role')
     lookback = int(request.form.get('lookback'))
@@ -538,6 +542,10 @@ def result_view():
     else:
         sid = request.args.get('strategy_id')
     strategy_id = request.args.get('strategy_id')
+
+    # Ensure plotly backend is set (fixes Railway deployment issue)
+    pd.options.plotting.backend = "plotly"
+
     sql="""select * from strategy where id=%s;"""
     conn = psycopg2.connect(**SQL_CONFIG)
     with conn: