Show similar earlier incidents and let notes be marked as the fix

The incident view gets a "Seen before" section from the server's new
/similar endpoint; an older server without it just shows nothing. C adds a
note as the resolution note, alongside c for a plain note. Needs the
server release that adds /similar.

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

internal/api/types.go

@@ -108,6 +108,10 @@ const (
 	EventResolved       = "resolved"
 	EventNote           = "note"
 
+	// A note marked as what fixed the incident. The server leads similar
+	// incidents with these.
+	EventResolutionNote = "resolution_note"
+
 	// Written when a team's dead man's switch stops reporting.
 	EventDeadmanSilent = "deadman_silent"
 
@@ -249,3 +253,15 @@ type APIKey struct {
 	CreatedAt  time.Time  `json:"created_at"`
 	LastUsedAt *time.Time `json:"last_used_at"`
 }
+
+// SimilarIncident is an earlier, resolved incident with the same signature
+// (alert name plus stable group labels) as the one being viewed. ResolutionNotes
+// are its "what fixed it" notes; NoteCount counts its plain notes.
+type SimilarIncident struct {
+	ID              int64           `json:"id"`
+	Title           string          `json:"title"`
+	TriggeredAt     time.Time       `json:"triggered_at"`
+	ResolvedAt      time.Time       `json:"resolved_at"`
+	NoteCount       int             `json:"note_count"`
+	ResolutionNotes []IncidentEvent `json:"resolution_notes"`
+}