Fix build-from-source on Windows: use JVM temp dir instead of hardcoded /tmp

The intermediate container projects :packages and :packages:react-native
are declared with projectDir = file("/tmp") to satisfy Gradle 9's
requirement that every project in a path have an existing folder. "/tmp"
is not an absolute path on Windows, so Gradle resolves it to a
non-existing <rootDir>\tmp and build-from-source fails at configuration
time. Use the JVM temp dir instead, which exists on every platform.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F7Mx2sWYCbJMwyTXaiXjbQ

Author: kraenhansen

packages/react-native/settings.gradle.kts

@@ -34,7 +34,10 @@ project(":packages:react-native:ReactAndroid:hermes-engine").projectDir =
 // As we build :packages:react-native:ReactAndroid, we need to declare the folders
 // for :packages and :packages:react-native as well as otherwise the build from
 // source will fail with a missing folder exception.
+// We point them at the JVM temp dir rather than a hardcoded "/tmp": the latter is
+// not an absolute path on Windows, where Gradle would resolve it to a
+// non-existing <rootDir>\tmp and fail at configuration time.
 
-project(":packages").projectDir = file("/tmp")
+project(":packages").projectDir = file(System.getProperty("java.io.tmpdir", "/tmp"))
 
-project(":packages:react-native").projectDir = file("/tmp")
+project(":packages:react-native").projectDir = file(System.getProperty("java.io.tmpdir", "/tmp"))