feat: add executeTool endpoint for direct plugin tool invocation

Adds POST /SmartAssistant/action/executeTool that accepts {tool, params, caseId}
and routes directly to the plugin tool handler via ActionExecutor. This allows
the AI Gateway to call plugin tools (like generate_direct_access_report) without
going through the conversation approval flow.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

manifest.json

@@ -3,7 +3,7 @@
     "module": "SmartAssistant",
     "description": "Unified AI Assistant for Legal CRM — floating chat with case memory, office alerts, and AI Gateway integration",
     "author": "klear",
-    "version": "2.6.0",
+    "version": "2.6.1",
     "acceptableVersions": [
         ">=8.0.0"
     ],