Add incident history page with date filter

Summary:
StatusPage.vue only shows the 5 most recent resolved incidents.
This adds a dedicated /incidents route with an IncidentHistory view
that lists all past incidents with a date range filter
(last 7 days / 30 days / 90 days / all).

Reuses the existing useIncidents composable and IncidentTimeline
component for consistency with StatusPage.

Test Plan:

1. Visit /incidents — page renders with title, filter buttons, and empty state message when no incidents exist
2. Create an incident via admin dashboard
3. Verify incident appears on /incidents under "Last 7 Days" and "All" filters
4. Verify "Last 30 Days" and "Last 90 Days" filters work
5. Click "Back to status" — navigates to /
6. Verify the same incident renders on StatusPage under Active Incidents using the same IncidentTimeline component

Reviewers: ieli

Reviewed By: ieli

Subscribers: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3980