Resolve an Extendy install ID to install info

Extendy calls this with the install ID it received via sub_id_10 on the offer (our external_id plus Extendy's static '::|00028' suffix). We strip the suffix, look up the matching install, and confirm it is ours.

external_id/sub_id_10 is our internal app_events.id (the click/install row's own UUID) — this system has no separate user record, so the event ID doubles as the user identifier and is set unconditionally at install time, regardless of the install's registration (lead) status.

Enabled only when the extendy_integration feature flag is on globally AND the owning account has extendy_enabled set (the company, for company-owned trackers, or the tracker's own user, for solo/individual trackers with no company) AND the install's stream (tracker) has extendy_enabled set; otherwise resolves as not found. The opt-in is per stream — traffic sources only record which ad source an install came from.