feat(infospace): add collection-level quality checks C1–C5 (S2.4)

Five concern checks: Redundancy (embedding/word overlap), Coverage
(FCA gap analysis), Coherence (graph connectivity), Consistency
(cycle detection), Granularity (Shannon entropy). Orchestrator runs
all or selected checks, CLI `markitect infospace check` command added.

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

markitect/infospace/checks/consistency.py

@@ -0,0 +1,58 @@
+"""
+C4 — Definitional consistency.
+
+Checks for cycles in the dependency graph and definitional conflicts
+between entities.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Dict, List, Optional
+
+from markitect.infospace.models import EntityMeta
+from markitect.prompts.dependencies.models import DependencyGraph
+
+
+@dataclass
+class ConsistencyReport:
+    """Results from consistency analysis."""
+
+    cycles: List[List[str]] = field(default_factory=list)
+    cycle_count: int = 0
+    entity_count: int = 0
+
+    def to_dict(self) -> dict:
+        return {
+            "concern": "C4",
+            "cycle_count": self.cycle_count,
+            "cycles": self.cycles,
+            "entity_count": self.entity_count,
+        }
+
+
+def check_consistency(
+    entities: List[EntityMeta],
+    graph: Optional[DependencyGraph] = None,
+) -> ConsistencyReport:
+    """Check definitional consistency.
+
+    Args:
+        entities: Entity metadata list.
+        graph: Optional dependency graph for cycle detection.
+
+    Returns:
+        :class:`ConsistencyReport` with cycles found.
+    """
+    n = len(entities)
+    cycles: List[List[str]] = []
+
+    if graph is not None and len(graph.nodes) > 0:
+        raw_cycles = graph.detect_cycles()
+        cycles = raw_cycles
+
+    return ConsistencyReport(
+        cycles=cycles,
+        cycle_count=len(cycles),
+        entity_count=n,
+    )