fix(tests): drop leading "/" on relative-URL fixture — platform-portable

`ProxyEndpoints_RecordingProjection_Relative_Url_And_Zero_Status_Encodes_As_Error`
asserted `ServerUrl == null` on the "URL has no scheme" branch. The
fixture URL `"/relative-only/no-scheme"` happens to satisfy
`Uri.TryCreate(..., UriKind.Absolute, out var u)` on Linux because
System.Uri treats leading "/" paths as POSIX file paths (resolves to
a `file://` URI). On Windows the same call returns false, leaving
`parsed` null — which is the branch the test wanted to drive.

Drop the leading slash so the URL is non-absolute on every platform.
The intent (verify the projection's null-parsed branch + encoded
HttpPath + queue dedup behaviour) is preserved; the test now passes
on linux-amd64 CI runners that fell over on commit 2347e7e.

Comment in source documents the trap so future contributors don't
re-add the leading slash.

Author: thomas-stegemann

tests/Kuestenlogik.Bowire.Tests/BranchCoverageGapsTests.cs

@@ -517,7 +517,13 @@ public async Task ProxyEndpoints_RecordingProjection_Relative_Url_And_Zero_Statu
             Id = 9002,
             CapturedAt = DateTimeOffset.FromUnixTimeMilliseconds(1234567890),
             Method = "POST",
-            Url = "/relative-only/no-scheme",
+            // No leading slash + no scheme: forces Uri.TryCreate(...,
+            // UriKind.Absolute) to return false on every OS. A leading
+            // "/" on Linux gets resolved to a file:// URI (POSIX path
+            // semantics in System.Uri) which makes the "parsed is null"
+            // branch unreachable on linux-arm64 CI runners — the test
+            // failed for exactly this on commit 2347e7e.
+            Url = "relative-only/no-scheme",
             ResponseStatus = 0, // network error
             LatencyMs = 0,
             RequestHeaders = new[]
@@ -546,7 +552,7 @@ public async Task ProxyEndpoints_RecordingProjection_Relative_Url_And_Zero_Statu
 
         // parsed is null -> ServerUrl stays null, httpPath = flow.Url
         Assert.Null(step.ServerUrl);
-        Assert.Equal("/relative-only/no-scheme", step.HttpPath);
+        Assert.Equal("relative-only/no-scheme", step.HttpPath);
         // parsed?.Host ?? "" -> Service ""
         Assert.Equal("", step.Service);
         // ResponseStatus == 0 -> "Error"