feat: WP-0003 — RoutingPolicy (FR-2) and HTTP serve mode (FR-1)

FR-2 RoutingPolicy:
- RoutingPolicy + RoutingRule dataclasses in llm_connect/routing.py
- resolve(task_type, estimated_cost_per_1k=None) with cost-cap fallback
- Exported from llm_connect.__init__; contract doc at contracts/functional/routing-policy.md
- 11 tests covering rule match, cost-cap, fallback, unknown type, no-match

FR-1 HTTP serve mode:
- LLMServer in llm_connect/server.py (stdlib http.server, zero extra deps)
- POST /execute + GET /health; CLI via python -m llm_connect.server
- [server] optional-dep group added to pyproject.toml
- Contract doc at contracts/functional/server.md
- 9 tests: health, round-trip, 400/404/500 errors, config forwarding
- Added "mock" provider to factory for CLI default

All 101 tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

llm_connect/factory.py

@@ -13,6 +13,7 @@ _PROVIDERS: Dict[str, str] = {
     "claude-code": "llm_connect.claude_code.ClaudeCodeAdapter",
     "gemini": "llm_connect.gemini.GeminiAdapter",
     "openai": "llm_connect.openai.OpenAIAdapter",
+    "mock": "llm_connect.adapter.MockLLMAdapter",
 }
 
 
@@ -57,4 +58,4 @@ def create_adapter(
     elif provider == "claude-code":
         return cls(model=model, **kwargs)
     else:
-        return cls(**kwargs)  # pragma: no cover
+        return cls(**kwargs)