feat(external-llm): standardize tiers and optimize model selection

- Rename tiers: opus/sonnet/haiku → frontier/mid-tier/lightweight
- Align with industry benchmarks (MMLU, GPQA, Chatbot Arena)
- Add /external command for LLM mode control
- Fix invoke.py timeout passthrough (now 600s default)

Tier changes:
- Promote gemini-2.5-pro to frontier (benchmark-validated)
- Demote glm-4.7 to mid-tier then removed (unreliable)
- Promote gemini-2.5-flash to mid-tier

New models added:
- gpt-5-mini, gpt-5-nano (GPT family coverage)
- grok-code (Grok/X family)
- glm-4.5-air (lightweight GLM)

Removed (redundant/unreliable):
- o3 (not available)
- glm-4.7 (timeouts)
- gpt-4o, big-pickle, glm-4.5-flash (redundant)

Final: 11 models across 3 tiers, 4 model families

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

state/component-registry.json

@@ -199,6 +199,15 @@
       ],
       "invokes": "skill:usage"
     },
+    "/external": {
+      "description": "Toggle and use external LLM mode (GPT-5.2, Gemini, etc.)",
+      "aliases": [
+        "/llm",
+        "/ext",
+        "/external-llm"
+      ],
+      "invokes": "command:external"
+    },
     "/README": {
       "description": "TODO",
       "aliases": [],