feat(centralui): rebrand web UI to ScadaBridge + technical-light theme

Rename the user-facing product name from ScadaLink to ScadaBridge across
the six display strings (browser title, sidebar brand, login + not-authorized
headings, dashboard welcome/subtitle). Namespaces, assemblies, config keys,
and _content/ScadaLink.CentralUI asset routes are unchanged.

Apply the technical-light design system: vendor theme.css + IBM Plex fonts
into the CentralUI RCL, include theme.css globally (after Bootstrap so its
--bs-* token overrides win), and restyle the layout chrome to a light
sidebar — white surface, hairline rules, ink text, accent-blue active item,
the brand accent mark. Page markup stays Bootstrap and inherits the warm
paper background, Plex type, accent, and hairline borders via the tokens.

Tests: build 0 warnings; bUnit 542 passed; Playwright 64 passed.

src/ScadaLink.CentralUI/Components/Layout/MainLayout.razor

@@ -17,7 +17,7 @@
         <NavMenu />
     </div>
 
-    <main class="flex-grow-1 p-3" style="background-color: #f8f9fa;">
+    <main class="flex-grow-1 p-3">
         @Body
     </main>
 </div>

src/ScadaLink.CentralUI/Components/Layout/NavMenu.razor

@@ -1,7 +1,7 @@
 @using ScadaLink.Security
 
 <nav class="sidebar d-flex flex-column">
-    <div class="brand">ScadaLink</div>
+    <div class="brand"><span class="mark">&#9646;</span> ScadaBridge</div>
 
     <div style="overflow-y:auto; flex:1 1 auto; min-height:0;">
         <ul class="nav flex-column">
@@ -147,15 +147,15 @@
 
     <AuthorizeView>
         <Authorized>
-            <div class="border-top border-secondary px-3 py-2">
+            <div class="border-top px-3 py-2">
                 <div class="d-flex justify-content-between align-items-center">
                     @* CentralUI-024: claim type resolved via JwtTokenService. *@
-                    <span class="text-light small">@context.User.GetDisplayName()</span>
+                    <span class="text-body-secondary small">@context.User.GetDisplayName()</span>
                     <form method="post" action="/auth/logout" data-enhance="false">
                         @* CentralUI-017: logout is a state-changing POST and is
                            CSRF-protected — the antiforgery token is required. *@
                         <AntiforgeryToken />
-                        <button type="submit" class="btn btn-outline-light btn-sm py-0 px-2">Sign Out</button>
+                        <button type="submit" class="btn btn-outline-secondary btn-sm py-0 px-2">Sign Out</button>
                     </form>
                 </div>
             </div>