Fix Players page KeyError + use_container_width deprecation

- Players page: fix regression_chart xg_col default (goals_p90 -> xg_p90)
- charts.py: make regression_chart defensive against missing columns
- All pages: replace use_container_width=True with width='stretch'
- Verified: all 5 pages render with zero errors via Playwright browser test

dashboard/pages/03_auction.py

@@ -151,13 +151,13 @@ def run():
         for r in ["P", "D", "C", "A"]:
             allocations[r] = sum(s["estimated_price"] for s in selected if s["role"] == r)
         fig = budget_waterfall(allocations)
-        st.plotly_chart(fig, use_container_width=True)
+        st.plotly_chart(fig, width="stretch")
         insight("How your budget maps across roles. Aim for ~15% GK, ~35% DEF, ~30% MID, ~20% FWD.")
 
     with c2:
         section("📈 Value Scatter")
         fig = value_scatter(players)
-        st.plotly_chart(fig, use_container_width=True)
+        st.plotly_chart(fig, width="stretch")
         insight("Top-right: high FV, high price. Bottom-right: value steals. "
                 "Bubble size = games played. Dashed lines = cost-per-FV-point isolines.")
 
@@ -186,7 +186,7 @@ def run():
     # ── Grid Auction Heatmap ──
     section("🔢 Grid Auction Simulator")
     fig = _grid_heatmap(players)
-    st.plotly_chart(fig, use_container_width=True)
+    st.plotly_chart(fig, width="stretch")
     insight("Green = good value at that bid multiplier. Red = overpaying. "
             "Bid at the 'green' multiplier for each player.")