Hook frontend build earlier in the publish chain

Per Copilot review on PR #740: BeforeTargets="Publish" runs after the
Publish target's dependencies, so file enumeration and copy already saw
a stale dist/ before our pnpm build ran.

Switch to two earlier hooks:
- Inject BuildFrontendForPublish into PublishDependsOn so it's the first
  dep of Publish (idiomatic .NET SDK pattern).
- BeforeTargets="PrepareForPublish;ComputeFilesToPublish" as a backstop
  in case the JS SDK invokes those outside the PublishDependsOn flow.

Both fire before any publish-time file collection, ensuring dist/ is
fresh when the SDK packages the StaticHost.

Author: slang25

src/frontend/frontend.esproj

@@ -12,8 +12,20 @@
 
   <!-- Ensure dist/ is freshly produced (and .twoslash-types/aspire.d.ts generated)
        whenever this project is published. The JS SDK's BuildCommand is gated off above,
-       so without this target a `dotnet publish` would package a stale or missing dist. -->
-  <Target Name="BuildFrontendForPublish" BeforeTargets="Publish">
+       so without this hook a `dotnet publish` would package a stale or missing dist.
+
+       Hook BEFORE the publish dependency chain runs:
+       - Inject into PublishDependsOn so we're the first dep of `Publish` itself.
+       - Belt-and-suspenders BeforeTargets on the early standard publish-chain targets
+         (PrepareForPublish / ComputeFilesToPublish), in case the JS SDK invokes those
+         outside the PublishDependsOn flow.
+       Hooking on `Publish` directly is too late — by then file enumeration and copy
+       have already collected the stale `dist/`. -->
+  <PropertyGroup>
+    <PublishDependsOn>BuildFrontendForPublish;$(PublishDependsOn)</PublishDependsOn>
+  </PropertyGroup>
+
+  <Target Name="BuildFrontendForPublish" BeforeTargets="PrepareForPublish;ComputeFilesToPublish">
     <Message Importance="high" Text="frontend.esproj: running 'pnpm install --frozen-lockfile' before publish" />
     <Exec Command="pnpm install --frozen-lockfile" WorkingDirectory="$(MSBuildProjectDirectory)" />
     <Message Importance="high" Text="frontend.esproj: running 'pnpm run build' before publish" />