Fix dashboard imports for Streamlit multi-page routing

- Add sys.path.insert at top of app.py and all 5 page files
- Fix .streamlit/config.toml CORS/XSRF conflict
- Remove duplicate st.set_page_config from page files
- Verified: all pages import cleanly, dashboard boots via streamlit run
- All 49 tests passing (31 original + 18 dashboard)

dashboard/app.py

@@ -3,6 +3,14 @@
 Multi-page Streamlit app. Run with: streamlit run dashboard/app.py
 """
 
+import sys
+from pathlib import Path
+
+# Ensure project root is on path so 'dashboard' imports resolve
+PROJECT_ROOT = Path(__file__).resolve().parent.parent
+if str(PROJECT_ROOT) not in sys.path:
+    sys.path.insert(0, str(PROJECT_ROOT))
+
 import streamlit as st
 
 from dashboard.viz.components import inject_css