feat: Java 21 modernization — render - #19

#``# Overview

Migrate COG-GTM/WorldWindJava from Java 11 to Java 21 LTS. This is a federal-grade, zero-breakage migration with atomic per-package PRs, full test verification before and after, and a rollup audit document. Use parallel child sessions to accelerate. All PRs target the fork's develop branch.

#``# PHASE 0: Pre-Migration Baseline (Sequential — MUST complete before anything else)

#``#``# Step 0.1: Capture Pre-Migration Baseline Metrics
Before ANY changes, on the develop branch with JDK 11:

`#` File count
find src -name "*.java" | wc -l
`#` Anonymous inner class counts
grep -rn "new Runnable()" --include="*.java" src/ | wc -l
grep -rn "new ActionListener()" --include="*.java" src/ | wc -l
grep -rn "new Callable()" --include="*.java" src/ | wc -l
grep -rn "new MouseListener()" --include="*.java" src/ | wc -l
grep -rn "new KeyListener()" --include="*.java" src/ | wc -l  
grep -rn "new ChangeListener()" --include="*.java" src/ | wc -l
grep -rn "new PropertyChangeListener()" --include="*.java" src/ | wc -l
grep -rn "new WindowListener()" --include="*.java" src/ | wc -l
`#` instanceof pattern-match candidates
grep -rn "instanceof " --include="*.java" src/ | wc -l
`#` Deprecated usage
grep -rn "`@`Deprecated" --include="*.java" src/ | wc -l
grep -rn "new Integer(" --include="*.java" src/ | wc -l
grep -rn "new Double(" --include="*.java" src/ | wc -l
grep -rn "new Float(" --include="*.java" src/ | wc -l
grep -rn "new Long(" --include="*.java" src/ | wc -l
grep -rn "new Boolean(" --include="*.java" src/ | wc -l

Save all counts to a file BASELINE-METRICS.txt at the repo root. This is your "before" snapshot.

#``#``# Step 0.2: Run the existing test suite under JDK 11

ant -f release-build.xml

Record pass/fail counts. This establishes that the test suite is green BEFORE migration.

#``# PHASE 1: Foundational JDK 21 Retarget PR (Sequential — Wave 0)

#``#``# Step 1.1: Create branch devin/java21-foundation
Make these changes ONLY (no code changes):

1. **`release-... (12653 chars truncated...)