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/generate_nvs_matrix.py

@@ -314,12 +314,21 @@ def generate_nvs_binary(csv_content: str, size: int) -> bytes:
                 return f.read()
 
         # Last resort: try as a module
-        subprocess.check_call([
-            sys.executable, "-m", "nvs_partition_gen", "generate",
-            csv_path, bin_path, hex(size)
-        ])
-        with open(bin_path, "rb") as f:
-            return f.read()
+        try:
+            subprocess.check_call([
+                sys.executable, "-m", "nvs_partition_gen", "generate",
+                csv_path, bin_path, hex(size)
+            ])
+            with open(bin_path, "rb") as f:
+                return f.read()
+        except (subprocess.CalledProcessError, FileNotFoundError):
+            print("ERROR: NVS partition generator tool not found.", file=sys.stderr)
+            print("Install: pip install esp-idf-nvs-partition-gen", file=sys.stderr)
+            print("Or set IDF_PATH to your ESP-IDF installation", file=sys.stderr)
+            raise RuntimeError(
+                "NVS partition generator not available. "
+                "Install: pip install esp-idf-nvs-partition-gen"
+            )
 
     finally:
         for p in (csv_path, bin_path):