OverrideHtmlAssetPlaceholders=true causes publish conflict for index.html when using StaticWebAssetBasePath

**Problem:**
When `OverrideHtmlAssetPlaceholders=true` and a non-empty `StaticWebAssetBasePath` is set (e.g., App1), the `OverrideHtmlAssetPlaceholders` task correctly removes the original index.html from the `StaticWebAsset` collection via its `HtmlFilesToRemove` output. However, the file is **not** removed from `ContentWithTargetPath`, causing `dotnet publish` to fail with `NETSDK1152: Found multiple publish output files with the same relative path` when hosting multiple Blazor WebAssembly apps in a single ASP.NET Core host.

**Root Cause:**
The `HtmlFilesToRemove` output only removes items from the static web assets pipeline. The original index.html remains in `ContentWithTargetPath` with index.html, ignoring the `StaticWebAssetBasePath` setting. When multiple Blazor WASM projects each have their own index.html, they all try to publish to the same path.

**Workaround:**
Add a target to manually remove index.html from `ContentWithTargetPath`:

```xml

```

Start by tracing how the OverrideHtmlAssetPlaceholders task's HtmlFilesToRemove output is applied and how ContentWithTargetPath is populated after AssignTargetPaths. Reproduce the publish conflict with multiple Blazor WebAssembly apps using a non-empty StaticWebAssetBasePath. Done means the original index.html no longer causes NETSDK1152 while the static web asset base path is respected.

Written by the indexing model from the issue text.