Fix static assets when running in non prod mode

[GarrettBeatty]

Fix static assets failing to load when ASPNETCORE_ENVIRONMENT is set to non-Production value

Fixes #2118

Description

When ASPNETCORE_ENVIRONMENT or DOTNET_ENVIRONMENT is set to anything other than Production (e.g., Development), the Lambda Test Tool's static assets (CSS, JS, BlazorMonaco) fail to load with 404 errors, rendering the web UI completely broken.

Root cause: In TestToolProcess.cs, static file serving was conditional on app.Environment.IsProduction(). In Production mode, an explicit PhysicalFileProvider pointing to AppContext.BaseDirectory/wwwroot was used, correctly serving files from the tool's install directory. In non-Production mode, the bare app.UseStaticFiles() was called instead, which relies on the static web assets manifest (staticwebassets.runtime.json). This manifest contains absolute paths from the build machine (source directories and NuGet cache paths) that don't exist on end-user machines, causing all static asset requests to return 404.

Fix: Always use the explicit PhysicalFileProvider to serve static files from the tool's install directory (AppContext.BaseDirectory/wwwroot), regardless of the environment. UseDeveloperExceptionPage() is still conditionally applied for non-Production environments.

Testing

Setup:

cd Tools\LambdaTestTool-v2\src\Amazon.Lambda.TestTool
dotnet pack -c Release
dotnet tool uninstall -g amazon.lambda.testtool
dotnet tool install -g amazon.lambda.testtool --version 0.13.0 --add-source bin\Release

Before fix — reproduce the bug:

cd C:\Users\<user>\Desktop  # navigate away from the repo source directory
$env:ASPNETCORE_ENVIRONMENT = 'Development'
dotnet-lambda-test-tool start --lambda-emulator-port 5099 --no-launch-window

From a second terminal:

(Invoke-WebRequest -Uri 'http://localhost:5099/app.css').StatusCode
# Returns 404 ❌

After fix — verify the fix:

# Re-pack and re-install with the fix applied, then:
cd C:\Users\<user>\Desktop
$env:ASPNETCORE_ENVIRONMENT = 'Development'
dotnet-lambda-test-tool start --lambda-emulator-port 5099 --no-launch-window

From a second terminal:

(Invoke-WebRequest -Uri 'http://localhost:5099/app.css').StatusCode
# Returns 200 ✅

Baseline — confirm no regression in Production mode:

$env:ASPNETCORE_ENVIRONMENT = $null
dotnet-lambda-test-tool start --lambda-emulator-port 5099 --no-launch-window

(Invoke-WebRequest -Uri 'http://localhost:5099/app.css').StatusCode
# Returns 200 ✅

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[GarrettBeatty]

the unit tests need this to pass. my guess is dotnet build does not auto copy the wwroot to the output directory.

However when i did the manual testing (as in the pr description), it seems like dotnet pack auto copy everything which is why this change wasn't needed then. But when i ran the tests i had to add in b559dd5