Fix Windows CI: detect Conan default profile on fresh runners

GitHub-hosted windows-latest has no ~/.conan2/profiles/default until
conan profile detect runs; also pin -pr:b=default in conan_init.

.github/workflows/windows_release.yml

@@ -37,6 +37,10 @@ jobs:
           python -m pip install --upgrade pip
           python -m pip install "conan>=2,<3"
           conan --version
+          # Fresh runners have no default profile; host==build for MSVC.
+          if (-not (Test-Path "$env:USERPROFILE\.conan2\profiles\default")) {
+            conan profile detect --force
+          }
 
       - name: Resolve version
         id: ver