fix(dashboard): admin-UI cleanup sweep

Family-wide admin-UI cleanup pass (scadaproj admin_ui_cleanup.md) applied to the
Blazor dashboard. Behaviour is unchanged throughout — no @onclick, disabled,
binding, auth gate, or arm->confirm flow was touched.

Uncontrolled error text is now truncated at the render site. Fault messages,
Galaxy load errors, and browse-tree load failures were rendered in full into
fixed-width table cells, where a long exception string blows out the column.
Each site gets DashboardDisplay.Abbreviate plus a title attribute carrying the
untruncated text, so nothing becomes unreachable. Abbreviate is length-checked
rather than a bare range slice: `value[..n]` on a shorter string throws and
takes the whole page render down with it. The two detail views whose entire
purpose is to show one fault in full — SessionDetailsPage and GalaxyPage's
Last Error — are deliberately left untruncated.

Two classes referenced from markup had no definition anywhere in the sheet.
.browse-stale-banner was inert; .tree-load-status was a real visual defect —
loading and failed-to-load rows sit among .tree-row siblings and carry the same
leading .tree-toggle-empty spacer, but that spacer only takes its width as a
flex item, so without a flex container those rows lost their indent.

Confirm/cancel pairs in ConfirmDialog and the API-key create form are now
btn-groups with role="group" and an aria-label, replacing margin-spaced loose
buttons.

Removes a paragraph on GalaxyPage naming internal RPCs (DiscoverHierarchy,
GetLastDeployTime) — implementation detail with no meaning to a dashboard
operator.

Verified in a real browser, not bUnit: full build clean, 879/879 tests, and a
live gate against a running dashboard with a genuine ~250-char SqlClient
exception as the erroring row. Results per check, including the checks that
could NOT be exercised without an x86 worker, are recorded in
docs/plans/2026-08-11-dashboard-ui-sweeps.md.

That plan doc also records a correction: this app is NOT Bootstrap-free. The
sweep brief said it was, citing the scadaproj index; libman.json pins
bootstrap 5.3.3 and App.razor:7 links it ahead of the theme. The stale claim had
already cost this app one skipped family sweep (scadaproj#2, the /admin/secrets
modal), so that modal was live-gated here too and passes.

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/Shared/BrowseTreeNodeView.razor

@@ -46,9 +46,11 @@
             }
             else if (Node.LoadState == BrowseLoadState.Error)
             {
-                <div class="tree-load-status text-danger">
+                @* Abbreviated: sibling tree rows are nowrap inside a fixed-height
+                   scroller, so a full COM/SQL error would stretch the whole pane. *@
+                <div class="tree-load-status text-danger" title="@Node.LoadError">
                     <span class="tree-toggle tree-toggle-empty"></span>
-                    <span>Failed to load: @Node.LoadError</span>
+                    <span>Failed to load: @DashboardDisplay.Abbreviate(Node.LoadError, 60)</span>
                 </div>
             }