feat(infospace,llm): agent ergonomics — entity lookup, model fallback, better errors

- `markitect infospace entity <name>`: single-entity lookup tolerating
  hyphens/underscores/case, with substring matching, ambiguity listing,
  and near-match hints. Prints slug, source path, domain, chapter, word
  count, VSM system, overall score, evaluator, and evaluation file path.
- `markitect infospace evaluate --model-fallback <model>`: if any
  entities fail with a rate-limit error, retry just those with a fresh
  adapter on the fallback model (different free-tier models have
  separate quota buckets).
- `markitect llm-check`: advisory when `OPENROUTER_API_KEY` is set but
  not used by the resolved provider; targeted hint when OpenRouter
  returns 401 (almost always a stale env key).
- `build_state`: raises `TypeError` with actionable message if passed a
  path instead of an `InfospaceConfig` — prior failure mode was a
  confusing `AttributeError` deep in the stack.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

markitect/infospace/state.py

@@ -131,6 +131,12 @@ def build_state(
     This is a convenience function that assembles the state object
     and optionally runs viability checks if *metrics* are provided.
     """
+    if not isinstance(config, InfospaceConfig):
+        raise TypeError(
+            f"build_state(config=...) expects an InfospaceConfig instance, "
+            f"got {type(config).__name__}. If you have a path, load the "
+            f"config first with load_infospace_config(path)."
+        )
     state = InfospaceState(
         config=config,
         entities=entities or [],