List incidents

Returns incidents for the authenticated account with optional filtering and pagination. Ordered by start time (newest first). A resolved incident older than 30 days is never returned here (issue #357) — this is a visibility floor enforced at read time, independent of how long the underlying row is physically kept (95 days, so the uptime-report worker and a status page's 90-day daily history both have enough lookback; see internal/retention/DECISIONS.md). An open incident is never hidden by this floor, however old it is.