feat: add signature tools for digital signature integration

Adds 4 Python tool registrations that call EspoCRM's SmartAssistant
executeTool endpoint with the DigitalSignature plugin tools:

- send_for_signature — send document for signing with auto-resolved signers
- check_signature_status — query status of signature requests
- remind_signers — send WhatsApp reminders to pending signers
- list_pending_signatures — show all awaiting signature requests

Tools are registered under the "signature" toolset, enabled by default.
Requires DigitalSignature extension v2.0.0+ on the EspoCRM side.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/services/agent_runner.py

@@ -12,6 +12,7 @@ from mcp_server.espocrm_client import EspoCrmClient
 from mcp_server.tools.crm_tools import register_crm_tools
 from mcp_server.tools.document_tools import register_document_tools
 from mcp_server.tools.legal_tools import register_legal_tools
+from mcp_server.tools.signature_tools import register_signature_tools
 from api.services.skills import register_skill_tools
 from api.services.memory import register_memory_tools
 from api.services.delegate import register_delegate_tool
@@ -80,6 +81,8 @@ class AgentRunner:
             register_document_tools(tools_registry, crm, case_id, context)
         if should_register_all or "legal" in (allowed_toolsets or []):
             register_legal_tools(tools_registry, crm, case_id, context)
+        if should_register_all or "signature" in (allowed_toolsets or []):
+            register_signature_tools(tools_registry, crm, case_id, user_id, context)
 
         # Phase 3 tools (only for main conversation, not child agents)
         if depth == 0: