Flag incidents that carry notes in the queue

A blue tag with the notebook icon and a count marks an incident with
working notes; a green one marks a note on what fixed it. Both let you
scan the queue for incidents that have more to say than their title,
without opening each one.

The incident list and detail JSON gain note_count and
resolution_note_count, counted in the same query that selects the
incident, so a list costs no extra request per row. The fields are
additive: terdut-tui and terdut-operator ignore them and need no change.

Claude-Session: https://claude.ai/code/session_016mBLURvJoMuUEr9cB2RpUN

internal/models/incident.go

@@ -66,6 +66,12 @@ type Incident struct {
 
 	ArchivedAt *time.Time `json:"archived_at,omitempty"`
 
+	// NoteCount and ResolutionNoteCount count the plain working notes and the
+	// "what fixed it" notes on the timeline, so a list can flag the incidents
+	// that carry extra information.
+	NoteCount           int `json:"note_count"`
+	ResolutionNoteCount int `json:"resolution_note_count"`
+
 	// Alerts is populated by GET /api/incidents/{id} only.
 	Alerts []Alert `json:"alerts,omitempty"`
 }