feat: add Java JRXML-to-PNG rendering pipeline with pixel-level SSIM comparison

- lib/java/: Java renderer (JrxmlRenderer) using JasperReports 6.21.0
  - JrxmlDebug for diagnostics, JrxmlGen for format reference
  - download_jars.sh for one-time dependency setup
- agent/nodes.py: _render_jrxml_to_png() and _compute_pixel_similarity()
  - Pixel comparison integrates into validate node (SSIM < 0.4 fails)
  - Pixel fidelity context injected into correct_jrxml for targeted fixes
- tests/test_pixel_comparison.py: 15 unit tests (render, SSIM, integration)
- .gitignore: exclude lib/java/*.jar, lib/java/*.class, tmp/
- CLAUDE.md: v11 changelog documenting the rendering pipeline
- All non-LLM tests pass (97/97)

lib/java/JrxmlRendererTest.java

@@ -0,0 +1,36 @@
+import net.sf.jasperreports.engine.*;
+import net.sf.jasperreports.engine.design.*;
+import net.sf.jasperreports.engine.xml.*;
+import java.io.*;
+
+public class JrxmlRendererTest {
+    public static void main(String[] args) throws Exception {
+        String path = args.length > 0 ? args[0] : "/tmp/test_render.jrxml";
+        File f = new File(path);
+        System.out.println("File: " + f.getAbsolutePath() + " exists=" + f.exists() + " len=" + f.length());
+        
+        // Read content to check XML validity
+        try (BufferedReader br = new BufferedReader(new FileReader(f))) {
+            String line;
+            int lineNum = 0;
+            while ((line = br.readLine()) != null && lineNum < 5) {
+                System.out.println("  L" + (++lineNum) + ": " + line);
+            }
+        }
+        
+        try {
+            System.out.println("Step 1: Loading JRXML...");
+            JasperDesign design = JRXmlLoader.load(f);
+            System.out.println("  OK - name=" + design.getName());
+        } catch (JRException e) {
+            System.err.println("JR ERROR: " + e.getMessage());
+            e.printStackTrace();
+        } catch (Exception e) {
+            System.err.println("GENERIC ERROR: " + e.getClass().getName() + ": " + e.getMessage());
+            e.printStackTrace();
+        } catch (Error e) {
+            System.err.println("FATAL ERROR: " + e.getClass().getName() + ": " + e.getMessage());
+            e.printStackTrace();
+        }
+    }
+}