- Fixes IDOR vulnerability by scoping conversation lookups by panel, participant, and tenant.

- Applies ownership checks across stream, chat load/delete/export, sidebar delete, and export service flows.

- Adds defense-in-depth hardening for audit and token usage conversation association.

- Adds comprehensive security regression tests for unauthorized read/write/delete/export and cross-panel access scenarios.

- Test suite verified passing after changes.

- Fixes issue #3.

- Special thanks to @Apollo139 for the responsible report, help, and collaboration.