feat(external-llm): add external LLM integration (fc-004)

Implements external LLM routing via opencode CLI for:
- GitHub Copilot (gpt-5.2, claude-sonnet-4.5, claude-haiku-4.5, o3, gemini-3-pro)
- Z.AI (glm-4.7 for code generation)
- OpenCode native (big-pickle)

Components:
- mcp/llm-router/invoke.py: Main router with task-based model selection
- mcp/llm-router/delegate.py: Agent delegation helper (respects external mode)
- mcp/llm-router/toggle.py: Enable/disable external-only mode
- mcp/llm-router/providers/: CLI wrappers for opencode and gemini

Features:
- Persistent toggle via state/external-mode.json
- Task routing: reasoning -> gpt-5.2, code-gen -> glm-4.7, long-context -> gemini
- Claude tier mapping: opus -> gpt-5.2, sonnet -> claude-sonnet-4.5, haiku -> claude-haiku-4.5
- Session-start hook announces when external mode is active
- Natural language toggle support via component registry

Plan: gleaming-routing-mercury

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

state/component-registry.json

@@ -143,6 +143,23 @@
         "block dangerous",
         "protect"
       ]
+    },
+    "external-mode": {
+      "description": "Toggle between Claude and external LLMs (Copilot, Z.AI, Gemini)",
+      "script": "~/.claude/mcp/llm-router/toggle.py",
+      "triggers": [
+        "external",
+        "use external",
+        "switch to external",
+        "external models",
+        "external only",
+        "use copilot",
+        "use opencode",
+        "back to claude",
+        "use claude again",
+        "disable external",
+        "external mode"
+      ]
     }
   },
   "commands": {

state/external-mode.json

@@ -0,0 +1,5 @@
+{
+  "enabled": false,
+  "activated_at": null,
+  "reason": null
+}

state/future-considerations.json

@@ -37,10 +37,11 @@
       "category": "integration",
       "title": "External LLM integration",
       "description": "Support for non-Claude models in the agent system",
-      "priority": "low",
-      "status": "deferred",
+      "priority": "medium",
+      "status": "planned",
       "created": "2024-12-28",
-      "notes": "For specialized tasks or cost optimization"
+      "plan": "gleaming-routing-mercury",
+      "notes": "Cloud APIs via subscription (Copilot, Z.AI, Gemini). Uses opencode/gemini CLIs. Session toggle for external-only mode."
     },
     {
       "id": "fc-005",

state/model-policy.json

@@ -113,5 +113,60 @@
       "default": "haiku",
       "escalate_on": ["insufficient_context", "reasoning_required", "user_dissatisfied"]
     }
+  },
+  "external_models": {
+    "github-copilot/gpt-5.2": {
+      "cli": "opencode",
+      "cli_args": ["-m", "github-copilot/gpt-5.2"],
+      "use_cases": ["reasoning", "fallback"],
+      "tier": "opus-equivalent"
+    },
+    "github-copilot/claude-sonnet-4.5": {
+      "cli": "opencode",
+      "cli_args": ["-m", "github-copilot/claude-sonnet-4.5"],
+      "use_cases": ["general", "fallback"],
+      "tier": "sonnet-equivalent"
+    },
+    "github-copilot/claude-haiku-4.5": {
+      "cli": "opencode",
+      "cli_args": ["-m", "github-copilot/claude-haiku-4.5"],
+      "use_cases": ["simple"],
+      "tier": "haiku-equivalent"
+    },
+    "zai-coding-plan/glm-4.7": {
+      "cli": "opencode",
+      "cli_args": ["-m", "zai-coding-plan/glm-4.7"],
+      "use_cases": ["code-generation"],
+      "tier": "sonnet-equivalent"
+    },
+    "github-copilot/gemini-3-pro-preview": {
+      "cli": "opencode",
+      "cli_args": ["-m", "github-copilot/gemini-3-pro-preview"],
+      "use_cases": ["long-context"],
+      "tier": "opus-equivalent"
+    },
+    "github-copilot/o3": {
+      "cli": "opencode",
+      "cli_args": ["-m", "github-copilot/o3"],
+      "use_cases": ["complex-reasoning"],
+      "tier": "opus-equivalent"
+    },
+    "opencode/big-pickle": {
+      "cli": "opencode",
+      "cli_args": ["-m", "opencode/big-pickle"],
+      "use_cases": ["general"],
+      "tier": "sonnet-equivalent"
+    }
+  },
+  "claude_to_external_map": {
+    "opus": "github-copilot/gpt-5.2",
+    "sonnet": "github-copilot/claude-sonnet-4.5",
+    "haiku": "github-copilot/claude-haiku-4.5"
+  },
+  "task_routing": {
+    "reasoning": "github-copilot/gpt-5.2",
+    "code-generation": "zai-coding-plan/glm-4.7",
+    "long-context": "github-copilot/gemini-3-pro-preview",
+    "default": "github-copilot/claude-sonnet-4.5"
   }
 }