fix(toolintent): exempt list_dir from reference-exists + rejection-loop breaker

Greenfield discovery/analyst stages thrashed on plane-2 REFERENCE_EXISTS
rejections: the model listed a not-yet-created dir (e.g. frontend/), got
hard-BLOCKED every round, and burned MAX_TOOL_ROUNDS without progress.

- New ToolCapability.DIRECTORY_LIST; ListDirTool declares it alongside
  FILE_READ. ReferenceExistsRule now exempts directory enumeration (a
  listing of an absent dir truthfully reports empty; only hallucinated
  file *reads* still fail loud). Dispatch stays on capability, not name.
- Stage-agnostic rejection-loop breaker in the tool loop: after 3 rounds
  where every tool call is rejected (BLOCKED/ERROR) with no success,
  force the model to produce its output. Covers JSON-emitting stages the
  read-loop breaker (file_written-only) never protected.

infrastructure/tools/filesystem/src/main/kotlin/com/correx/infrastructure/tools/filesystem/ListDirTool.kt

@@ -66,7 +66,8 @@ class ListDirTool(
         put("required", buildJsonArray {})
     }
     override val tier: Tier = Tier.T1
-    override val requiredCapabilities: Set<ToolCapability> = setOf(ToolCapability.FILE_READ)
+    override val requiredCapabilities: Set<ToolCapability> =
+        setOf(ToolCapability.FILE_READ, ToolCapability.DIRECTORY_LIST)
     override val paramRoles: Map<String, ParamRole> = mapOf("path" to ParamRole.PATH)
 
     override fun validateRequest(request: ToolRequest): ValidationResult {