feat(grid): range-select finalize opens add form, writes via store.Add

@@ -0,0 +1,48 @@
+package grid
+
+import (
+	"testing"
+
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+func TestRangeTimes(t *testing.T) {
+	m := loaded(&fakeStore{}) // slot 30, window 07:00.. → row0=07:00
+	s, e := m.rangeTimes(0, 1)
+	if s != "07:00" || e != "08:00" {
+		t.Errorf("rangeTimes(0,1)=%s..%s, want 07:00..08:00", s, e)
+	}
+	s, e = m.rangeTimes(0, 0)
+	if s != "07:00" || e != "07:30" {
+		t.Errorf("single-slot rangeTimes(0,0)=%s..%s, want 07:00..07:30", s, e)
+	}
+}
+
+func TestSelectionAddCallsStoreAdd(t *testing.T) {
+	f := &fakeStore{}
+	m := loaded(f)
+	// enter ACTIVITY, anchor at 0, extend to 1, finalize
+	nm, _ := m.Update(special(tea.KeyLeft)) // ensure ACTIVITY
+	nm, _ = nm.(Model).Update(key(" "))     // anchor
+	nm, _ = nm.(Model).Update(special(tea.KeyDown))
+	nm, _ = nm.(Model).Update(key(" ")) // finalize → opens form
+	mm := nm.(Model)
+	if !mm.editing || !mm.adding || mm.form == nil {
+		t.Fatalf("finalize should open the add form")
+	}
+	if mm.fv.Start != "07:00" || mm.fv.End != "08:00" {
+		t.Errorf("form prefilled %s..%s, want 07:00..08:00", mm.fv.Start, mm.fv.End)
+	}
+	// fill required fields then Ctrl+S
+	mm.fv.Project, mm.fv.Desc = "ARCHER", "new work"
+	nm, _ = mm.Update(special(tea.KeyCtrlS))
+	if len(f.added) != 1 {
+		t.Fatalf("store.Add not called; added=%d", len(f.added))
+	}
+	if f.added[0].Project != "ARCHER" || f.added[0].Description != "new work" {
+		t.Errorf("added wrong entry: %+v", f.added[0])
+	}
+	if f.added[0].Start.Hour() != 7 || f.added[0].End.Hour() != 8 {
+		t.Errorf("added times wrong: %v..%v", f.added[0].Start, f.added[0].End)
+	}
+}