style(centralui): full-app bg-light/bg-white -> theme-aware utility sweep (M10 residual)

T34c only fixed the bounded modal-surface offenders. Bootstrap 5.3's bg-light
and bg-white are fixed light values that do NOT flip under [data-bs-theme=dark],
so every remaining use was a dark-mode contrast break. 35 swaps across 19 files:

  surface / <pre> / <code>  bg-light                -> bg-body-secondary
  panel                     bg-white                -> bg-body
  neutral badge             bg-light text-dark      -> bg-secondary-subtle text-secondary-emphasis
  muted badge / input group bg-light text-muted     -> bg-body-secondary text-body-secondary

DELIBERATELY LEFT (7 sites): the neutral member of a status-badge switch or
ternary whose siblings are all solid, non-theme-aware colours (bg-success,
bg-danger, bg-warning) — swapping only the neutral one to a subtle token breaks
the visual weight of the set, so these stay until the whole family is retoned:
  Topology.razor:513 (Current badge) and :588 (InstanceState.NotDeployed)
  InstanceConfigure.razor:1520 (same InstanceState switch)
  NotificationReport.razor StatusBadgeClass fallback
  TransportImport.razor ConflictKind badge fallback
  SecuredWrites.razor text-bg-light fallback (a text-bg-* family with no
    theme-aware member at all)
  Health.razor:377 depth ternary
Also untouched by design: SchemaBuilder.razor:88 (already bg-light-subtle,
theme-aware), bg-dark text-light console panels, and site.css / #reconnect-modal.

InstanceConfigure.razor is edited concurrently elsewhere; its change here is 5
pure class-string swaps on existing lines, no reflow. No test asserted any of
these classes. Also marks all four M10 residuals done in the plan doc.

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/DataConnectionForm.razor

@@ -111,7 +111,7 @@
                     Backup endpoint
                     @if (!_showBackup)
                     {
-                        <span class="badge bg-light text-muted border ms-2">Optional</span>
+                        <span class="badge bg-body-secondary text-body-secondary border ms-2">Optional</span>
                     }
                 </h6>
                 @if (!_showBackup)