[EPAC-2280]: Generate APNs-visible live-vote copy

[riddim-developer-bot]

Scope

• Generate a display-ready LiveVoteNotification from required live-vote payload fields.
• Serialize APNs requests with aps.alert.title and aps.alert.body while preserving source identifiers as custom fields.
• Reject malformed and incomplete live-vote payloads deterministically before dispatcher construction.
• Add the push-notification-dispatcher module to the PR backend test gate.

Bugfix SPEC

• Spec: Linear issue EPAC-2280
• Trace ID: N/A - Linear implementation ticket

Testing notes

• Automated tests run:
  • cd backend/push-notification-dispatcher && /usr/local/go/bin/go test ./...
  • cd backend/push-notification-dispatcher && /usr/local/go/bin/go test -tags=acceptance ./...
• Manual verification: Not run; this change affects backend-generated APNs payload content and does not add an iOS GUI surface.

Sample APNs payload

{"aps":{"alert":{"title":"Vote result posted","body":"Division 42 result: carried."}},"division_id":42,"parliament":45,"session":1,"result":"carried","status":"concluded"}

Screenshots

N/A - backend APNs payload surface only.

Related issue

• Closes: EPAC-2280

Release-Note: Live-vote push notifications now include visible neutral vote result copy.