feat(fusion_accounting_ai): 5 new customer follow-up AI tools

Adds Task 17 tool layer:
- fusion_list_overdue
- fusion_get_partner_followup_detail
- fusion_generate_followup_text
- fusion_send_followup
- fusion_get_partner_risk_score

Tools register through TOOL_DISPATCH and degrade with a clear
error message when fusion_accounting_followup is not installed.
5 TransactionCase tests added (78 total).

Made-with: Cursor

fusion_accounting_ai/services/tools/__init__.py

@@ -11,12 +11,13 @@ from .reporting import TOOLS as REPORTING_TOOLS
 from .audit import TOOLS as AUDIT_TOOLS
 from .financial_reports import TOOLS as FINANCIAL_REPORTS_TOOLS
 from .asset_management import TOOLS as ASSET_MANAGEMENT_TOOLS
+from .customer_followup import TOOLS as CUSTOMER_FOLLOWUP_TOOLS
 
 TOOL_DISPATCH = {}
 for tools_dict in [
     BANK_RECON_TOOLS, HST_TOOLS, AR_TOOLS, AP_TOOLS, JOURNAL_TOOLS,
     MONTH_END_TOOLS, PAYROLL_TOOLS, INVENTORY_TOOLS, ADP_TOOLS,
     REPORTING_TOOLS, AUDIT_TOOLS, FINANCIAL_REPORTS_TOOLS,
-    ASSET_MANAGEMENT_TOOLS,
+    ASSET_MANAGEMENT_TOOLS, CUSTOMER_FOLLOWUP_TOOLS,
 ]:
     TOOL_DISPATCH.update(tools_dict)