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/inject_fault.py

@@ -46,8 +46,12 @@ def connect_monitor(sock_path: str, timeout: float = CMD_TIMEOUT) -> socket.sock
         banner = s.recv(RECV_BUFSIZE).decode("utf-8", errors="replace")
         if banner:
             pass  # Consume silently
+        else:
+            print(f"WARNING: Connected to {sock_path} but received no banner data. "
+                  f"QEMU monitor may not be ready.", file=sys.stderr)
     except socket.timeout:
-        pass  # No banner is OK
+        print(f"WARNING: Connected to {sock_path} but timed out waiting for banner "
+              f"after {timeout}s. QEMU monitor may be unresponsive.", file=sys.stderr)
 
     return s