perf(worker): switch to workstation GC to cut idle memory

Sdk.Web defaults to Server GC, one heap per core with a ~350 MB
gen0 budget each — an idle worker sat at ~230 MB private. Workstation
GC drops that to ~40 MB with no server-side concurrency to lose.

src/ClaudeDo.Worker/ClaudeDo.Worker.csproj

@@ -25,6 +25,9 @@
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <ApplicationIcon>ClaudeTaskWorker.ico</ApplicationIcon>
+    <!-- Sdk.Web defaults to Server GC: one heap per core (22 here) with a ~350 MB gen0 budget,
+         so an idle worker sat at ~230 MB private. Workstation GC: ~40 MB. -->
+    <ServerGarbageCollection>false</ServerGarbageCollection>
   </PropertyGroup>
 
   <ItemGroup>