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/config.py

@@ -0,0 +1,108 @@
+"""
+LLM configuration and API key resolution.
+"""
+
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Optional, Dict, Any
+import os
+
+
+@dataclass
+class LLMConfig:
+    """Configuration for an LLM adapter.
+
+    Attributes:
+        provider: Backend identifier (``"openrouter"`` or ``"claude-code"``).
+        model: Model name / path sent to the provider.
+        api_key: Resolved API key (may be ``None`` for CLI backends).
+        api_base: Base URL for HTTP-based providers.
+        claude_cli_path: Path to the ``claude`` CLI binary.
+        timeout_seconds: Per-request timeout.
+        max_retries: Number of retry attempts on transient errors.
+        extra: Arbitrary provider-specific overrides.
+    """
+
+    provider: str = "openrouter"
+    model: str = "anthropic/claude-sonnet-4"
+    api_key: Optional[str] = None
+    api_base: str = "https://openrouter.ai/api/v1"
+    claude_cli_path: str = "claude"
+    timeout_seconds: int = 300
+    max_retries: int = 3
+    extra: Dict[str, Any] = field(default_factory=dict)
+
+
+def resolve_api_key(
+    explicit: Optional[str] = None,
+    env_var: str = "OPENROUTER_API_KEY",
+    key_file_paths: Optional[list[Path]] = None,
+) -> Optional[str]:
+    """Return an API key from the first available source.
+
+    Resolution order:
+      1. *explicit* argument (passed directly by caller)
+      2. Environment variable *env_var*
+      3. First readable file in *key_file_paths* whose content is non-empty
+
+    Returns ``None`` if no key can be found.
+    """
+    if explicit:
+        return explicit
+
+    from_env = os.environ.get(env_var)
+    if from_env:
+        return from_env.strip()
+
+    for path in key_file_paths or []:
+        try:
+            text = path.read_text().strip()
+            if text:
+                return text
+        except OSError:
+            continue
+
+    return None
+
+
+def find_project_root(start: Optional[Path] = None) -> Optional[Path]:
+    """Walk up from *start* (default CWD) looking for ``pyproject.toml``.
+
+    Returns the directory containing the marker file, or ``None``.
+    """
+    current = (start or Path.cwd()).resolve()
+    for directory in [current, *current.parents]:
+        if (directory / "pyproject.toml").is_file():
+            return directory
+    return None
+
+
+def load_config(
+    provider: str = "openrouter",
+    model: Optional[str] = None,
+    api_key: Optional[str] = None,
+    **overrides: Any,
+) -> LLMConfig:
+    """Build an :class:`LLMConfig` with sensible defaults.
+
+    For the ``openrouter`` provider the API key is resolved via
+    :func:`resolve_api_key` (env var → project-root key file).
+    """
+    root = find_project_root()
+    key_file_paths = [root / "apikey-openrouter.txt"] if root else []
+
+    resolved_key = api_key
+    if provider == "openrouter" and not resolved_key:
+        resolved_key = resolve_api_key(
+            explicit=None,
+            env_var="OPENROUTER_API_KEY",
+            key_file_paths=key_file_paths,
+        )
+
+    defaults: Dict[str, Any] = {
+        "provider": provider,
+        "model": model or "anthropic/claude-sonnet-4",
+        "api_key": resolved_key,
+    }
+    defaults.update(overrides)
+    return LLMConfig(**defaults)