fix/build: resolve project path to absolute and surface empty-build failures

Two coupled papercuts in the level-2 build path:

- A relative `--input` doubled the project path. The build runs with its working
  directory set to the project root, but gradleBuild passed the raw (relative)
  `-p <projectPath>` (maven was already absolutized, gradle was not), so it
  resolved against the root to `<root>/<root>`, the build failed, and zero
  application classes loaded. Normalize the path to absolute once at the
  buildProjectAndStreamClassFiles entry point so every downstream tool is
  consistent.

- A failed build was swallowed: buildProjectAndStreamClassFiles returns an empty
  list (never null) on failure, but ScopeUtils only guarded `== null`, so
  analysis proceeded with an empty scope and died later with a cryptic WALA
  "Could not create entrypoint callsites" error. Guard on emptiness too and
  report the real cause (build failed / no compiled classes / bad input path).

Author: rahlk

src/main/java/com/ibm/cldk/utils/BuildProject.java

@@ -194,7 +194,11 @@ private static boolean buildProject(String projectPath, String build) {
      * @return true if the streaming was successful, false otherwise.
      */
     public static List<Path> buildProjectAndStreamClassFiles(String projectPath, String build) throws IOException {
-        return buildProject(projectPath, build) ? classFilesStream(projectPath) : new ArrayList<>();
+        // Normalize to an absolute path up front: the build runs with its working directory set to the
+        // project root, so a relative `-p`/`-f` would resolve against it and double the path (e.g.
+        // `<root>/<root>`), making the build fail and yielding zero application classes.
+        String absProjectPath = Paths.get(projectPath).toAbsolutePath().normalize().toString();
+        return buildProject(absProjectPath, build) ? classFilesStream(absProjectPath) : new ArrayList<>();
     }
 
     private static boolean mkLibDepDirs(String projectPath) {

src/main/java/com/ibm/cldk/utils/ScopeUtils.java

@@ -105,8 +105,12 @@ public static AnalysisScope createScope(String projectPath, String applicationDe
 
     List<Path> applicationClassFiles = BuildProject.buildProjectAndStreamClassFiles(projectPath, build);
     Log.debug("Application class files: " + String.valueOf(applicationClassFiles.size()));
-    if (applicationClassFiles == null) {
-      Log.error("No application classes found.");
+    // An empty list (not null) is what a failed build returns, so guard on emptiness too — otherwise
+    // analysis proceeds with zero application classes and fails later with a cryptic WALA entrypoint
+    // error instead of surfacing the real cause (the project build failed or produced no classes).
+    if (applicationClassFiles == null || applicationClassFiles.isEmpty()) {
+      Log.error("No application classes found — the project build may have failed or produced no "
+          + "compiled classes. Check the build output above and that the input path is correct.");
       throw new RuntimeException("No application classes found.");
     }
     Log.info("Adding application classes to scope.");