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/__init__.py

@@ -0,0 +1,40 @@
+"""
+markitect.llm — LLM integration adapters for MarkiTect.
+
+Provides concrete :class:`LLMAdapter` implementations backed by
+OpenRouter (HTTP) and Claude Code CLI (subprocess).
+
+Quick start::
+
+    from markitect.llm import create_adapter
+
+    adapter = create_adapter("openrouter", model="anthropic/claude-sonnet-4")
+    response = adapter.execute_prompt(prompt, run_config)
+"""
+
+from markitect.llm.factory import create_adapter
+from markitect.llm.openrouter import OpenRouterAdapter
+from markitect.llm.claude_code import ClaudeCodeAdapter
+from markitect.llm.config import LLMConfig, load_config
+from markitect.llm.exceptions import (
+    LLMError,
+    LLMConfigurationError,
+    LLMAPIError,
+    LLMRateLimitError,
+    LLMTimeoutError,
+    LLMSubprocessError,
+)
+
+__all__ = [
+    "create_adapter",
+    "OpenRouterAdapter",
+    "ClaudeCodeAdapter",
+    "LLMConfig",
+    "load_config",
+    "LLMError",
+    "LLMConfigurationError",
+    "LLMAPIError",
+    "LLMRateLimitError",
+    "LLMTimeoutError",
+    "LLMSubprocessError",
+]