Fix account alias and run title display

[yvette-carlisle]

Summary

• remove Alex from generated account aliases and use configured account names for dashboard/app account display fallbacks
• keep fixed-account labels named when emails are hidden and no row is currently matched
• prevent live run activity from replacing issue titles with generic Agent Run labels; fall back to the issue key when no real title exists

Verification

• cargo test -p decodex operator_dashboard_run_activity_preserves_snapshot_detail_fields
• cargo test -p decodex account
• cargo +nightly fmt --all -- --check
• swift build --package-path apps/decodex-app
• git diff --check
• Browser smoke: dashboard mock shows Taylor/Jamie/Maya with no Alex; controlled dashboard event renders PUB-923 instead of Agent Run and preserves Snapshot issue title after live activity