feat: add dev preview dashboard showcasing all 12 new ML models

- New page 06_dev_preview.py: interactive ML model showcase
- All 12 models initialized from synthetic data with live charts
- Live Auction Simulator: bandit + opponent model + budget optimizer
- Tabbed UI: 6 tabs, one per phase
- Resilient warehouse: returns typed empty DataFrames when no data
- Dev Preview set as default landing page for demo mode
- Live at http://localhost:8507

dashboard/app.py

@@ -19,6 +19,7 @@ from dashboard.viz.components import inject_css
 from dashboard.viz.template import stub_render  # triggers template registration
 
 PAGES = {
+    "🔬 Dev Preview": "dashboard.pages.06_dev_preview",
     "⚽ Matchday": "dashboard.pages.01_matchday",
     "👤 Players": "dashboard.pages.02_players",
     "💰 Auction": "dashboard.pages.03_auction",