Fixes /admin 404 by building the admin SPA before dotnet publish, not via an MSBuild target

The BuildAndCopyAdminFrontend MSBuild target (BeforeTargets=Publish) never actually
worked: files it created after project evaluation were silently absent from the
publish output, and forcing them in via an explicit Content item collided with the
SDK's own static-web-asset resolution. Verified locally with a clean obj/bin and a
fresh node_modules - every deploy so far genuinely shipped without wwwroot/admin.
Moves the frontend build + copy into its own CI step ahead of dotnet publish, so the
SDK's ordinary wwwroot handling picks it up with no custom MSBuild involved.

Also fixes unreadable <code> badges on the website placeholder page (no explicit
text color, relying on inherited body color pairing unreliably with the badge
background).

src/SlpModularCms.Api/Extensions/WebsitePlaceholder.html

@@ -20,7 +20,7 @@
         }
         @media (prefers-color-scheme: dark) {
             body { background: #141414; color: #ededed; }
-            code { background: #262626; }
+            code { background: #262626; color: #141414; }
             a { color: #ff6b6b; }
         }
         main { max-width: 34rem; }
@@ -28,6 +28,7 @@
         p { margin: 0 0 1rem; }
         code {
             background: #ececec;
+            color: #1a1a1a;
             padding: 0.15em 0.4em;
             border-radius: 4px;
             font-family: ui-monospace, "Cascadia Code", Consolas, monospace;

src/SlpModularCms.Api/SlpModularCms.Api.csproj

@@ -35,22 +35,21 @@
     </ItemGroup>
 
     <!--
-      Builds the CMS admin SPA (frontend/) and copies its output into wwwroot/admin so it's served
-      at the /admin path (see Program.cs). Only runs on `dotnet publish`, not on every dev build.
-      The public website ('/') lives outside this repo and is deployed into wwwroot separately.
+      The admin SPA (frontend/) is served at /admin (see Program.cs) from wwwroot/admin, but is
+      deliberately NOT built by an MSBuild target hooked to Build/Publish here. Both attempts tried
+      (a plain <Copy> after a BeforeTargets="Publish" pnpm build, and an explicit <Content> item with
+      a custom TargetPath) were verified locally to fail: the SDK's wwwroot static-web-asset item set
+      is fixed at project evaluation time, before any target runs, so files a target creates afterward
+      are silently absent from the publish output; and forcing them in as a Content item collided with
+      the SDK's own static-web-asset resolution ("Two assets found targeting the same path with
+      incompatible asset kinds: admin/admin/..."), reproducibly, even from a clean obj/bin and a fresh
+      node_modules. The only combination that published wwwroot/admin correctly was the files already
+      physically existing on disk *before* dotnet publish/build ever runs — see the CI workflow
+      (continuous_integration.yaml), which builds frontend/ and copies frontend/dist into
+      wwwroot/admin as its own step, ahead of `dotnet publish`. Do the same locally before publishing:
+      run `pnpm install` then `pnpm build` inside frontend/, then copy
+      `frontend/dist/*` into `wwwroot/admin/` (that folder is gitignored, so nothing to clean up
+      afterward), then `dotnet publish` picks it up via the SDK's ordinary wwwroot handling.
     -->
-    <PropertyGroup>
-      <AdminFrontendDir>$(MSBuildProjectDirectory)/../../frontend</AdminFrontendDir>
-    </PropertyGroup>
-
-    <Target Name="BuildAndCopyAdminFrontend" BeforeTargets="Publish">
-      <Message Importance="high" Text="Building CMS admin frontend ($(AdminFrontendDir))..." />
-      <Exec Command="pnpm install --frozen-lockfile" WorkingDirectory="$(AdminFrontendDir)" />
-      <Exec Command="pnpm build" WorkingDirectory="$(AdminFrontendDir)" />
-      <ItemGroup>
-        <AdminFrontendFiles Include="$(AdminFrontendDir)/dist/**/*" />
-      </ItemGroup>
-      <Copy SourceFiles="@(AdminFrontendFiles)" DestinationFolder="$(MSBuildProjectDirectory)/wwwroot/admin/%(RecursiveDir)" SkipUnchangedFiles="true" />
-    </Target>
 
 </Project>