feat: live charge limit, identity retunes, btop assets (product calls)

- Charge limit: udev GROUP=users on threshold; menu applies sysfs live
  and persists state; boot/AC oneshot prefers live theme-state.json.
- Look & Feel: Reset wallpaper (auto); Theme/next/night light already there.
- NVIDIA first-class wrappers deferred past v1 (keep #59 comments).
- Identity taste: white, lumon, hackerman, matte-black, miasma.
- Hand btop.theme for identity + boreal/executive-slate/neon-glass.

Verified: V0 contrast; V1 battery-charge-limit VM. V3 live sysfs on laptop.

themes/matte-black.json

@@ -10,7 +10,7 @@
     "surface": "#333333",
     "overlay": "#8a8a8d",
     "text": "#bebebe",
-    "subtext": "#bebebe",
+    "subtext": "#9a9a9d",
     "muted": "#8a8a8d",
     "accent": "#e68e0d",
     "accentAlt": "#D35F5F",