feat(rootly): add On Event trigger for incident timeline events

[SolariSystems]

Summary

Adds the On Event trigger for the Rootly integration, enabling workflows to react when incident timeline events are created or updated.

• Listens for incident_event.created and incident_event.updated webhook events
• 7 optional configuration filters: visibility, event kind, incident status, severity, service, team, event source
• Emits payload with: id, event content, kind, visibility, occurred_at, created_at, user_display_name, incident
• Frontend trigger renderer with metadata display for configured filters
• 22 tests covering signature verification, event filtering, all optional filters, and combined filter behavior

Changes

Backend:

• on_event.go — Trigger implementation with OnEventConfiguration, HandleWebhook (signature verification + event type + optional filters), matchesEventFilters (case-insensitive matching, service/team match by name or slug)
• on_event_test.go — 22 tests: signature (3), JSON parsing (1), event type filtering (2), visibility (2), event kind (1), incident status (2), severity (1), service (2), team (1), combined filters (2), setup (4)
• example_data_on_event.json — Example webhook payload
• example.go — ExampleData for OnEvent
• rootly.go — Register OnEvent in Triggers()

Frontend:

• on_event.ts — Trigger renderer with title/subtitle from event content, metadata display for filters
• index.ts — Register onEvent trigger renderer

Test plan

• All 22 new tests pass (go test ./pkg/integrations/rootly/... -count=1)
• All 30 existing Rootly tests continue to pass
• go vet clean
• Video demo of setup and working trigger

Closes #2820

[cursor]

You have run out of free Bugbot PR reviews for this billing cycle. This will reset on March 12.

To receive reviews on all of your PRs, visit the Cursor dashboard to activate Pro and start your 14-day free trial.

[forestileao]

Closing it, duplicate of #3150