feat(skills): integrate NVIDIA/skills as a trusted skills hub tap

NVIDIA's verified skills catalog (https://github.com/NVIDIA/skills) ships
NVIDIA-signed skills for CUDA-X, AIQ, cuOpt, cuPyNumeric, DeepStream, NeMo,
NemoClaw and the Skill Card Generator — each bundle carrying a detached
`skill.oms.sig` signature, a governance `skill-card.md`, and `evals/`. The
sync pipeline drops any skill missing those artifacts before publishing.

Changes:
- tools/skills_hub.py: add NVIDIA/skills to GitHubSource.DEFAULT_TAPS so
  it lights up in `hermes skills browse`, `hermes skills search <q>`, the
  twice-daily skills-index build, and the docs-site Skills Hub page
  (https://hermes-agent.nousresearch.com/docs/skills) automatically.
- tools/skills_guard.py: add NVIDIA/skills to TRUSTED_REPOS so installs
  resolve to trust_level="trusted" (looser install policy than community).
- website/scripts/extract-skills.py: map the `github` source id to a
  friendly "NVIDIA" pill label for the docs hub page.
- website/src/pages/skills/index.tsx: register the NVIDIA pill (green
  #76b900) and slot it into SOURCE_ORDER after HuggingFace.
- website/docs/user-guide/features/skills.md (+ zh-Hans i18n): document
  the new default tap and the expanded trusted-repos list.
- tests/tools/test_skills_guard.py: assert NVIDIA/skills resolves to
  "trusted" (including the skills-sh-wrapped form).
- tests/tools/test_skills_hub.py: invariant — every TRUSTED_REPOS entry
  must be reachable via GitHubSource.DEFAULT_TAPS (prevents future
  trusted repos from being declared but never browseable).

Validation:
- Live GitHub fetch: `src.fetch('NVIDIA/skills/skills/aiq-deploy')` pulled
  17 files including SKILL.md (13 KB), skill-card.md, skill.oms.sig, and
  the full references/ + evals/ tree. trust_level="trusted".
- Live inspect resolved name, description, and trust correctly.
- All 193 existing skills_guard + skills_hub tests still pass.

website/src/pages/skills/index.tsx

@@ -163,6 +163,13 @@ const SOURCE_CONFIG: Record<
     border: "rgba(251, 191, 36, 0.2)",
     icon: "\u{1F917}",
   },
+  NVIDIA: {
+    label: "NVIDIA",
+    color: "#76b900",
+    bg: "rgba(118, 185, 0, 0.08)",
+    border: "rgba(118, 185, 0, 0.25)",
+    icon: "\u{25B6}",
+  },
   VoltAgent: {
     label: "VoltAgent",
     color: "#facc15",
@@ -207,6 +214,7 @@ const SOURCE_ORDER = [
   "Anthropic",
   "OpenAI",
   "HuggingFace",
+  "NVIDIA",
   "skills.sh",
   "ClawHub",
   "browse.sh",