feat(llm): add LLM integration module with OpenRouter and Claude Code adapters

Implements markitect/llm/ package with concrete LLMAdapter implementations:
- OpenRouterAdapter: HTTP via urllib with retry/backoff on 429/5xx
- ClaudeCodeAdapter: subprocess-based Claude CLI with stdin piping
- Factory pattern: create_adapter("openrouter") or create_adapter("claude-code")
- API key resolution chain: constructor > env var > project-root key file
- 42 unit tests, 2 integration tests (gated on API key / CLI availability)

Also adds the infospace-with-history example with Wealth of Nations VSM
analysis pipeline, templates, schemas, source chapters, and processed
output for chapters 1-2. process_chapters.py now supports --provider
and --model flags for automatic LLM-driven processing.

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

markitect/llm/factory.py

@@ -0,0 +1,58 @@
+"""
+Factory for creating LLM adapters by provider name.
+"""
+
+from typing import Optional, Dict, Any
+
+from markitect.prompts.execution.llm_adapter import LLMAdapter
+from markitect.llm.exceptions import LLMConfigurationError
+
+# Lazy imports to avoid pulling in every adapter at module load time.
+_PROVIDERS: Dict[str, str] = {
+    "openrouter": "markitect.llm.openrouter.OpenRouterAdapter",
+    "claude-code": "markitect.llm.claude_code.ClaudeCodeAdapter",
+}
+
+
+def create_adapter(
+    provider: str = "openrouter",
+    model: Optional[str] = None,
+    api_key: Optional[str] = None,
+    system_prompt: Optional[str] = None,
+    **kwargs: Any,
+) -> LLMAdapter:
+    """Instantiate an :class:`LLMAdapter` for the given *provider*.
+
+    Args:
+        provider: ``"openrouter"`` or ``"claude-code"``.
+        model: Model name (passed to the adapter constructor).
+        api_key: Explicit API key (OpenRouter only).
+        system_prompt: Optional system prompt (OpenRouter only).
+        **kwargs: Extra keyword arguments forwarded to the adapter.
+
+    Returns:
+        A ready-to-use :class:`LLMAdapter` instance.
+
+    Raises:
+        LLMConfigurationError: If *provider* is not recognised.
+    """
+    if provider not in _PROVIDERS:
+        known = ", ".join(sorted(_PROVIDERS))
+        raise LLMConfigurationError(
+            f"Unknown LLM provider {provider!r}. Choose from: {known}",
+            context={"provider": provider},
+        )
+
+    # Lazy import
+    fqn = _PROVIDERS[provider]
+    module_path, class_name = fqn.rsplit(".", 1)
+    import importlib
+    mod = importlib.import_module(module_path)
+    cls = getattr(mod, class_name)
+
+    if provider == "openrouter":
+        return cls(model=model, api_key=api_key, system_prompt=system_prompt, **kwargs)
+    elif provider == "claude-code":
+        return cls(model=model, **kwargs)
+    else:
+        return cls(**kwargs)  # pragma: no cover