Werkzeugkasten: Zugangsdaten je Einheit (#692)

A unit holds credentials for its members, by tool and setting - needed once,
not once per agent, and other units never get them.

- UnitConfig.credentials, protected by ConfigSecrets like every secret.
- OrgChart.ToolSettingsFor: an agent's own settings, completed by the nearest
  unit up that holds the value; own non-empty values win; no tool is granted.
  Used for runs, tool jobs and preflight probes.
- OrgAdministration.SetUnitCredential, PUT /organisation/units/{id}/credentials;
  the view lists held settings, never values.
- Templates never carry unit credentials; they are named instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ClawdDotNet.Core/Engine/AgentEngine.cs

@@ -1853,9 +1853,12 @@ public sealed class AgentEngine : IAgentMessageRouter, Staging.IFrozenCallExecut
         AgentConfig agentConfig, string instanceId, string toolName, CancellationToken ct,
         DelegationChain? chain = null, string? runId = null)
     {
-        var toolConfig = agentConfig.Tools.TryGetValue(toolName, out var cfg)
-            ? cfg.AsReadOnly()
-            : new Dictionary<string, object?>().AsReadOnly();
+        // #692: completed by the credentials the agent's unit holds for the tool.
+        var toolConfig = OrganisationProvider?.Invoke() is { } org
+            ? org.ToolSettingsFor(agentConfig, toolName)
+            : agentConfig.Tools.TryGetValue(toolName, out var cfg)
+                ? cfg.AsReadOnly()
+                : new Dictionary<string, object?>().AsReadOnly();
 
         var toolLogger = _loggerFactory.CreateLogger($"ClawdDotNet.Tools.{toolName}.Execution");
         var baseChain = chain ?? DelegationChain.Root(agentConfig.AgentId);