Pin build SDK to 10.0.204 to restore blazor.web.js

SDK 10.0.300 published a static-assets endpoints manifest without
blazor.web.js, so MapStaticAssets returned 404 for the Blazor boot script
in production. With no boot script the interactive circuit never starts
and every page renders static — buttons and dropdowns (e.g. user role
changes) do nothing. SDK 10.0.204 is verified to publish blazor.web.js
(physical file + manifest entry) against the 10.0.8 runtime.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -1,6 +1,12 @@
 # Base images pinned to exact patch for reproducible builds. Floating `:10.0` tags
 # drift; a stale/pre-GA SDK base silently drops the Blazor framework static assets
 # (blazor.web.js) from the publish manifest → 404 in production. Bump deliberately.
+#
+# SDK 10.0.300 reintroduced exactly that regression: it published an endpoints
+# manifest without blazor.web.js, so MapStaticAssets 404'd the boot script and the
+# whole app rendered static (no interactive circuit on any page). SDK 10.0.204 is
+# verified to publish blazor.web.js (physical file + manifest entry) and pairs with
+# the 10.0.8 runtime below.
 FROM mcr.microsoft.com/dotnet/aspnet:10.0.8 AS base
 WORKDIR /app
 EXPOSE 8080
@@ -9,7 +15,7 @@ RUN apt-get update \
     && apt-get install -y --no-install-recommends curl \
     && rm -rf /var/lib/apt/lists/*
 
-FROM mcr.microsoft.com/dotnet/sdk:10.0.300 AS build
+FROM mcr.microsoft.com/dotnet/sdk:10.0.204 AS build
 WORKDIR /src
 COPY ["SharepointToolbox.Web.csproj", "."]
 RUN dotnet restore