Let the API image see the trimmer pin, so its restore stops breaking on each .NET servicing release

The API Dockerfile copied four of the five root build files before restoring and left out Directory.Build.targets, which pins Microsoft.NET.ILLink.Tasks. The image's locked-mode restore therefore asked for whatever ILLink its SDK bundled, and when sdk:10.0-noble moved to 10.0.401 (ILLink 10.0.12) it failed with NU1004 against lock files that correctly say 10.0.11 - while ci.yml, which sees the pin, stayed green.

src/DodoSSH.Api/Dockerfile

@@ -2,9 +2,18 @@
 #
 #   docker build -f src/DodoSSH.Api/Dockerfile .
 #
-# Directory.Build.props, Directory.Packages.props, NuGet.config and global.json all sit at
-# the root and all four are load-bearing here — central package management means a csproj
-# alone does not name a single version, and a build that cannot see them resolves nothing.
+# Directory.Build.props, Directory.Build.targets, Directory.Packages.props, NuGet.config and
+# global.json all sit at the root and all five are load-bearing here — central package
+# management means a csproj alone does not name a single version, and a build that cannot see
+# them resolves nothing.
+#
+# Directory.Build.targets is the one that is easy to forget, because leaving it out breaks
+# nothing until the day it does: it pins the version of the trimmer the SDK adds to
+# DodoSSH.Contracts and DodoSSH.Crypto by itself (see the comment there). Without it the restore
+# below asks for whatever ILLink the image's SDK bundles, which matches the lock files only
+# until .NET ships a servicing release — and then this image fails with NU1004 while ci.yml,
+# which does see the pin, stays green. That is how it was found: sdk:10.0-noble moved to
+# 10.0.401 (ILLink 10.0.12) and this build broke with no commit touching a package.
 
 # ---------------------------------------------------------------------------------------
 # Build
@@ -26,7 +35,7 @@ WORKDIR /src
 # dependency change and by nothing else. Every project in DodoSSH.Api's reference closure
 # has to be here — restore walks ProjectReference, and a missing csproj fails the graph
 # rather than skipping a node.
-COPY global.json NuGet.config Directory.Build.props Directory.Packages.props ./
+COPY global.json NuGet.config Directory.Build.props Directory.Build.targets Directory.Packages.props ./
 COPY src/DodoSSH.Api/DodoSSH.Api.csproj                       src/DodoSSH.Api/
 COPY src/DodoSSH.Api/packages.lock.json                       src/DodoSSH.Api/
 COPY src/DodoSSH.Contracts/DodoSSH.Contracts.csproj           src/DodoSSH.Contracts/