fix(scripts): improve usability across all ADR-061 QEMU testing scripts

- Add --help/-h flags to all 4 shell scripts with usage, env vars, examples
- Add prerequisite checks with install hints (apt/brew/pip) for missing tools
- Standardize exit codes (0=PASS, 1=WARN, 2=FAIL, 3=FATAL) across all scripts
- Standardize MESH_TIMEOUT to QEMU_TIMEOUT with backward compatibility
- Add SKIP_BUILD precheck for missing flash image in qemu-esp32s3-test.sh
- Add argparse to validate_qemu_output.py (was using raw sys.argv)
- Improve error messages in generate_nvs_matrix.py with NVS tool install hints
- Add socket connection warnings in inject_fault.py connect_monitor()
- Add example output epilog to check_health.py --help
- Add glossary (14 terms) and quick-start section to ADR-061
- Add GDB debugging walkthrough to ADR-061 Layer 4
- Fix stat portability in CI workflow (stat -c%s -> portable file_size())
- Add -type f to find commands in CI workflow

Co-Authored-By: claude-flow <ruv@ruv.net>

scripts/check_health.py

@@ -256,6 +256,13 @@ def run_health_checks(
 def main():
     parser = argparse.ArgumentParser(
         description="QEMU Post-Fault Health Checker — ADR-061 Layer 9",
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+        epilog=(
+            "Example output:\n"
+            "  [HEALTHY] t=30s frames=150 (5.0 fps) crashes=0 heap_err=0 wdt=0 reboots=0\n"
+            "  \n"
+            "  VERDICT: Firmware is healthy. No critical issues detected."
+        ),
     )
     parser.add_argument(
         "--log", required=True,