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.

build/ventoy.json

@@ -0,0 +1,25 @@
+{
+  "ventoy": {
+    "timeout": 30,
+    "default_image": "rescue.iso",
+    "menu_style": "LIST",
+    "theme": {
+      "file": "/ventoy/theme/theme.txt",
+      "gfxmode": "1920x1080"
+    },
+    "persistence": [
+      {
+        "image": "/ISO/rescue.iso",
+        "backend": "/persistence/rescue.dat"
+      }
+    ],
+    "control": [
+      { "VTOY_DEFAULT_SEARCH_ROOT": "/ISO" },
+      { "VTOY_MENU_TIMEOUT": "0" },
+      { "VTOY_TREE_VIEW_MENU_STYLE": "1" },
+      { "VTOY_FILT_DOT_UNDERSCORE_FILE": "1" },
+      { "VTOY_SORT_CASE_SENSITIVE": "0" },
+      { "VTOY_MAX_SEARCH_LEVEL": "3" }
+    ]
+  }
+}