R-1112: open the family store when the controller starts

Found on demo-hp with 0.325.0-rc.1: the store (and so the conversion of an old family.json) opened only on the
first family request; a box nobody visits through a family gate kept the session values. OpenFamilyStore from
main, one INFO line with the count. TestR1112_StartConvertsTheFamilyFile, TestR1112_MainOpensTheFamilyStore,
red-proved.

Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/family/family.go

@@ -88,6 +88,8 @@ type Store struct {
 	mu       sync.Mutex
 	members  map[string]*Member
 	sessions map[string]Session
+
+	converted int // sessions Open found stored the old way (R-1112) — ConvertedAtOpen, for the start-up log line
 }
 
 var (
@@ -134,6 +136,7 @@ func Open(dir string) (*Store, error) {
 		}
 		s.sessions[se.FP] = se
 	}
+	s.converted = converted
 	if converted > 0 {
 		s.mu.Lock()
 		err := s.saveLocked()
@@ -306,6 +309,14 @@ func (s *Store) Verify(name, password string) bool {
 	return bcrypt.CompareHashAndPassword([]byte(hash), []byte(password)) == nil
 }
 
+// ConvertedAtOpen is how many sessions Open found stored the old way and rewrote as fingerprints (0 for a nil store).
+func (s *Store) ConvertedAtOpen() int {
+	if s == nil {
+		return 0
+	}
+	return s.converted
+}
+
 // NewSession starts a session for member ("" = the household) and returns its cookie value — the only time the value
 // exists outside the browser; the store keeps its Fingerprint. It refuses a member who does not exist.
 func (s *Store) NewSession(member string) (string, error) {