build:usb-image — Final USB image assembly script, Ventoy config, and Hermes agent runtime structure

- build/usb-image.sh: Main USB image assembler with artifact validation,
  ISO building, disk image creation, and USB write support
- build/ventoy.json: Ventoy configuration for multi-boot USB
- src/hermes/config.yaml: Portable Hermes agent configuration
- src/hermes/autorun.sh: Auto-launch script with full diagnostic pipeline
- Makefile: Build system with iso/image/check/clean/write targets

Generates fallback stubs for any diagnostic modules whose upstream
build tasks haven't completed yet, ensuring the image boots even
during active development.

src/diagnostics/__init__.py

@@ -0,0 +1,28 @@
+"""
+Hermes Portable Rescue — Diagnostic modules.
+
+Modules
+-------
+hardware : HardwareInventory
+    CPU, RAM, GPU, disk enumeration and SMART health checks.
+stress : RAMStressTester, CPUStressTester, GPUStressTester
+    Stress-test wrappers (available when stress.py is present).
+
+Each submodule exposes a ``run() -> dict`` for JSON and a
+``text_report() -> str`` for human consumption.
+"""
+from src.diagnostics.hardware import HardwareInventory
+
+try:
+    from src.diagnostics.stress import (
+        CPUStressTester,
+        GPUStressTester,
+        RAMStressTester,
+        run_all_stress_tests,
+    )
+except ImportError:
+    pass
+
+__all__ = [
+    "HardwareInventory",
+]