✨ Configuration - Allow Tiger to run on meetings with external participants but filter external recipients from notifications

As per @CalumSimpson in Sprint 6 Review — "It's totally fine if Tiger runs, as long as it doesn't send out the message to an external person. It should go to SSW and then they can choose to share it."

Pain

Currently Tiger skips processing entirely when external participants are detected. This means no dashboards are generated for spec reviews or other meetings with clients.

Context

As per @suiyangqiu in Sprint 6 Review — "We're relying entirely on the fact that Tiger can't send messages to anyone outside of SSW's tenant. It's not something built in where Tiger is only sending it out to SSW."

Acceptance Criteria

1. Tiger continues to process meetings that include external participants (generate dashboard, save transcript)
2. Notifications are only sent to SSW internal participants — external participants are excluded from the recipient list
3. The filtering is done at the application level (not relying on tenant restrictions)
4. SSW participants can choose to share the dashboard link with externals manually if they wish

The issue names no files or tests; start by tracing where external participants currently cause meeting processing to be skipped and where notification recipients are assembled. Verify the processing flow still generates the dashboard and saves the transcript, then confirm notification recipients exclude external participants while internal SSW participants remain included.