fix(ui): invariant decimals + LocaleState test isolation + drawer offset + bundled Plotly

Cross-cutting polish that surfaced while Phase 8 was being implemented:

* Invariant-culture formatting on every decimal ToString("0.00" / "0.##")
  (OddsCell, OddsTimeline, SeverityBadge, AnomalyEvidence,
  Pages/Events/Detail) — previously the comma/dot decimal separator
  switched with the locale and broke tabular alignment + tests.

* LocaleState constructor no longer mutates process-wide ambient culture;
  apply only happens through Set(...). Stops parallel bUnit test runs
  leaking ru-RU into each other's threads.

* MainLayout: drawer-open state now offsets main content / footer / appbar
  by the drawer width (248px) so the sidebar no longer overlaps content.
  Mobile breakpoint (≤720px) keeps the original full-width layout.

* wwwroot/index.html (Marathon.UI RCL): switched from Plotly CDN to the
  bundled "_content/Plotly.Blazor/plotly-2.35.3.min.js" — works offline
  and matches the Plotly.Blazor 5.4.1 version pin.

* Marathon.Hosts.WpfBlazor/wwwroot/index.html: host-level page that
  BlazorWebView's HostPage attribute resolves to. Same Plotly bundle,
  no autostart="false" (BlazorWebView auto-starts).

src/Marathon.UI/Pages/Events/Detail.razor

@@ -105,7 +105,7 @@
                                     <td>@BetTypeLabel(row.Type)</td>
                                     <td>@SideLabel(row.Side)</td>
                                     <td class="m-mono" style="text-align: right;">@FormatThreshold(row.Threshold)</td>
-                                    <td class="m-mono" style="text-align: right; font-weight: 500;">@row.Rate.ToString("0.00")</td>
+                                    <td class="m-mono" style="text-align: right; font-weight: 500;">@row.Rate.ToString("0.00", System.Globalization.CultureInfo.InvariantCulture)</td>
                                 </tr>
                             }
                         </tbody>
@@ -334,6 +334,8 @@
         _ => s.ToString(),
     };
 
-    private static string FormatRate(decimal? r) => r is { } v ? v.ToString("0.00") : "—";
-    private static string FormatThreshold(decimal? v) => v is { } x ? x.ToString("0.##") : "—";
+    private static string FormatRate(decimal? r) =>
+        r is { } v ? v.ToString("0.00", System.Globalization.CultureInfo.InvariantCulture) : "—";
+    private static string FormatThreshold(decimal? v) =>
+        v is { } x ? x.ToString("0.##", System.Globalization.CultureInfo.InvariantCulture) : "—";
 }