Add tool governance allowlist

[baraajack]

Summary

Adds tenant-isolated, agent-scoped tool governance.

Included

• tool_permissions table with RLS enforcement
• Agent-scoped tool allow-list configuration
• ToolPermissionRepository for grant lookup and updates
• Authorization deny path for tools outside configured grants
• New decision reason: "denied: tool not allowed"
• Tool permission management API endpoint
• Kill switch precedence preserved
• Budget precedence preserved
• Decision logging preserved before response
• Idempotency preserved via existing decision log path

Authorization Order

1. Kill Switch
2. Budget Controls
3. Tool Governance
4. Static Deny Test
5. Default Allow

Not Included

• Policy DSL
• Tool catalog
• Tool groups
• Argument inspection
• SDK changes
• Human approval
• Dashboards or reporting
• Changes to ingestion or observability paths

Validation

• Authorization service tests
• Authorization endpoint tests
• Full test suite passes (125 passed)
• Tenant isolation preserved
• Idempotent deny verified
• Kill switch override verified
• Budget precedence verified