Show notes from similar earlier incidents

Each incident gets a signature: the alert name plus the group labels that
say what is broken, minus the ones that only say where it ran (instance,
pod, container, ...). GET /api/incidents/{id}/similar returns resolved
incidents in the same team with the same signature that have notes.

Notes can be marked as the resolution note, "what fixed it", either with a
resolution field on resolve or pinned on a note. Those lead the similar
list, show on the incident page as "Seen before", and the triggered
notification carries the latest one.

Claude-Session: https://claude.ai/code/session_01MMados3BD1oSjevHxbmVqU

internal/api/router.go

@@ -112,6 +112,7 @@ func NewRouter(db *sql.DB, notify NotifyConfig, cfg config.Config) http.Handler
 		r.Get("/api/incidents/{id}", handleGetIncident(db))
 		r.Get("/api/incidents/{id}/alerts", handleIncidentAlerts(db))
 		r.Get("/api/incidents/{id}/timeline", handleIncidentTimeline(db))
+		r.Get("/api/incidents/{id}/similar", handleIncidentSimilar(db))
 		r.Post("/api/incidents/{id}/acknowledge", handleIncidentAcknowledge(db))
 		r.Delete("/api/incidents/{id}/acknowledge", handleIncidentUnacknowledge(db))
 		r.Post("/api/incidents/{id}/resolve", handleIncidentResolve(db))