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/download_jars.sh

@@ -0,0 +1,33 @@
+#!/bin/bash
+# Download JasperReports 6.21.0 and dependencies for JRXML-to-PNG rendering.
+# Run this once after cloning the repo.
+set -e
+
+BASE="https://repo1.maven.org/maven2"
+
+JARS=(
+  "net/sf/jasperreports/jasperreports/6.21.0/jasperreports-6.21.0.jar"
+  "commons-logging/commons-logging/1.3.5/commons-logging-1.3.5.jar"
+  "org/apache/commons/commons-collections4/4.5.0/commons-collections4-4.5.0.jar"
+  "commons-beanutils/commons-beanutils/1.10.1/commons-beanutils-1.10.1.jar"
+  "org/apache/commons/commons-lang3/3.17.0/commons-lang3-3.17.0.jar"
+  "commons-digester/commons-digester/2.1/commons-digester-2.1.jar"
+  "com/lowagie/itext/2.1.7/itext-2.1.7.jar"
+  "org/jfree/jfreechart/1.5.5/jfreechart-1.5.5.jar"
+  "org/eclipse/jdt/ecj/3.38.0/ecj-3.38.0.jar"
+)
+
+for jar in "${JARS[@]}"; do
+  fname=$(basename "$jar")
+  if [ -f "$fname" ]; then
+    echo "SKIP: $fname (exists)"
+  else
+    echo "DOWNLOAD: $fname"
+    curl -sL -o "$fname" "$BASE/$jar"
+  fi
+done
+
+echo ""
+echo "All JARs ready. Compile with:"
+echo "  javac -cp \"jasperreports-6.21.0.jar;...\" JrxmlRenderer.java"
+echo "  java  -cp \".;jasperreports-6.21.0.jar;...\" JrxmlRenderer input.jrxml output.png 2.0"