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/personal-assistant/general-instructions.json

@@ -20,6 +20,18 @@
       "status": "active",
       "added": "2026-01-04"
     },
+    {
+      "id": "f6a7b8c9-0123-45fa-1234-666666666666",
+      "instruction": "After reinstalling gmail-mcp package, run ~/.claude/patches/apply-gmail-auth-patch.sh to restore auto re-auth on token expiry.",
+      "status": "active",
+      "added": "2026-01-09"
+    },
+    {
+      "id": "a7b8c9d0-1234-56ab-2345-777777777777",
+      "instruction": "Homelab repo is at ~/Code/active/devops/homelab/homelab (canonical). ~/.claude/repos/homelab is a symlink to it. Always use the canonical path for new work.",
+      "status": "active",
+      "added": "2026-01-09"
+    },
     {
       "id": "b2c3d4e5-6789-01bc-def0-222222222222",
       "instruction": "Git workflow: See CLAUDE.md for full process. Use rebase merges, not merge commits.",