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>

commands/external.md

@@ -0,0 +1,89 @@
+---
+name: external
+description: Toggle and use external LLM mode (GPT-5.2, Gemini, etc.)
+aliases: [llm, ext, external-llm]
+---
+
+# External LLM Mode
+
+Route requests to external LLMs via opencode or gemini CLI.
+
+## Usage
+
+```
+/external                   # Show current status
+/external on [reason]       # Enable external mode
+/external off               # Disable external mode
+/external invoke <prompt>   # Send prompt to default model
+/external invoke --model <model> <prompt>   # Send to specific model
+/external invoke --task <task> <prompt>     # Route by task type
+/external models            # List available models
+```
+
+## Implementation
+
+### Status
+```bash
+~/.claude/mcp/llm-router/toggle.py status
+```
+
+### Toggle On/Off
+```bash
+~/.claude/mcp/llm-router/toggle.py on --reason "reason"
+~/.claude/mcp/llm-router/toggle.py off
+```
+
+### Invoke
+```bash
+~/.claude/mcp/llm-router/invoke.py --model MODEL -p "prompt" [--json]
+~/.claude/mcp/llm-router/invoke.py --task TASK -p "prompt" [--json]
+```
+
+## Available Models by Tier
+
+### Frontier (strongest)
+| Model | Provider | Best For |
+|-------|----------|----------|
+| `github-copilot/gpt-5.2` | opencode | reasoning, fallback |
+| `github-copilot/gemini-3-pro-preview` | opencode | long context, reasoning |
+| `gemini/gemini-2.5-pro` | gemini | long context, reasoning |
+
+### Mid-tier (general purpose)
+| Model | Provider | Best For |
+|-------|----------|----------|
+| `github-copilot/claude-sonnet-4.5` | opencode | general, fallback |
+| `github-copilot/gemini-3-flash-preview` | opencode | fast |
+| `zai-coding-plan/glm-4.7` | opencode | code generation |
+| `opencode/big-pickle` | opencode | general |
+| `gemini/gemini-2.5-flash` | gemini | fast |
+
+### Lightweight (simple tasks)
+| Model | Provider | Best For |
+|-------|----------|----------|
+| `github-copilot/claude-haiku-4.5` | opencode | simple tasks |
+
+## Task Routing
+
+| Task | Routes To | Tier |
+|------|-----------|------|
+| `reasoning` | github-copilot/gpt-5.2 | frontier |
+| `code-generation` | github-copilot/gemini-3-pro-preview | frontier |
+| `long-context` | gemini/gemini-2.5-pro | frontier |
+| `fast` | github-copilot/gemini-3-flash-preview | mid-tier |
+| `general` (default) | github-copilot/claude-sonnet-4.5 | mid-tier |
+
+## State Files
+
+- Mode state: `~/.claude/state/external-mode.json`
+- Model policy: `~/.claude/state/model-policy.json`
+
+## Examples
+
+```
+/external on testing        # Enable for testing
+/external invoke "Explain k8s pods"   # Use default model (mid-tier)
+/external invoke --model github-copilot/gpt-5.2 "Complex analysis"  # frontier
+/external invoke --task code-generation "Write a Python function"   # routes to frontier
+/external invoke --task fast "Quick question"                       # routes to mid-tier
+/external off               # Back to Claude
+```