feat: enhance agent settlement features and improve data access controls

- Added new section in AGENTS.md detailing learned workspace facts for better understanding of settlement processes.
- Updated AgentNodeDestroyController to remove unnecessary checks for admin users.
- Enhanced AgentSettlement controllers to assert permissions for finance adjustments and bill operations.
- Improved query scopes in AgentSettlement services to ensure proper data access based on admin roles.
- Refactored methods in SettlementPartyEnrichment for better bill row enrichment and data handling.
- Introduced new methods in AdminAgentSettlementScope for managing agent node visibility and finance adjustments.

lang/en/validation_business.php

@@ -27,6 +27,7 @@ return [
     'parent_overdue' => 'The parent agent has overdue bills. This operation is not allowed.',
     'period_already_open' => 'A period with this date range is already open. Close it instead of opening again.',
     'period_site_has_open' => 'This site already has an open period. Close it before opening a new one.',
+    'period_overlaps_existing' => 'This period overlaps an existing one. Adjust the start and end dates.',
     'period_not_found' => 'Settlement period not found or not accessible.',
     'period_already_closed' => 'This period is already closed.',
     'share_snapshot_missing' => 'Some ledger rows are missing share snapshots. Complete draw settlement first.',