Security hardening release for Filament Copilot.

This release addresses multiple authorization and access-control issues:
- Enforce authorizeUsing() callback in chat + stream flows.
- Apply ownership/tenant/panel scoping for conversation load, delete, export, audit, and rate-limit paths.
- Respect Filament authorization in discovery and tool execution (canAccess/canView).
- Enforce managementGuard() for Copilot management resources and dashboard.
- Add dedicated security regression tests for unauthorized access scenarios.

Special thanks to @Apollo139 for the responsible disclosure and clear security reports that helped improve package safety.