Remote Tab Opener Manager 8.4.0 adds a secure inter-extension API for official RTO add-ons.

What changed:
- Added a native external add-on API for trusted RTO extensions.
- Added a Trust Policy that verifies the calling extension before accepting external requests.
- Added secure capability reporting for official add-ons such as RTO Project Bridge.
- RTO original remains the authority for RTO Lock, allowlist checks, capabilities and browser execution.
- Unknown external extensions are refused by default.
- Direct allowlist mutation is not exposed to add-ons.
- Normal RTO usage remains unchanged when no add-on is installed.

Compatibility:
- Existing RTO 8.x workflows remain compatible.
- Existing page helpers and SDK usage remain compatible.
- The new add-on API is additive and does not require users to install RTO Project Bridge.