Play Framework

Fix compilation error page rendering and restore test infrastructure

- Fix cascade failure where 500 error page couldn't render when app
  code had compilation errors: GroovyTemplateCompiler.endTag() now
  catches CompilationException from getAssignableClasses(FastTags),
  and PlayHandler.serve500 falls back to a static HTML error page
  with error details instead of "Internal Error (check logs)"
- Fix log4j.properties syntax errors (invalid logger name format)
  and load framework default config as fallback so log output
  includes the logger category name (fixing 'ERROR play' pattern
  expected by integration tests)
- Restore testModule and customJars directories needed by
  just-test-cases functional tests (were incorrectly deleted
  with sample apps)
- Restore build-test-modules target in build.xml

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>