Add a Value slot to dialogue.Slots

router.Slots already carries the fact payload; the dialogue copy did not, so a clarifying answer had nowhere to put it. InheritSlots carries it like Key.
Reviewer: check the new inherit block does not overwrite a filled value.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

internal/dialogue/session.go

@@ -21,6 +21,7 @@ type Slots struct {
 	Time    time.Time
 	HasTime bool
 	Key     string
+	Value   string // payload for a fact key, mirrors router.Slots.Value
 	HasKey  bool
 	Text    string
 	Fn      string
@@ -104,6 +105,9 @@ func InheritSlots(prev, cur Slots) Slots {
 		out.Key = prev.Key
 		out.HasKey = true
 	}
+	if out.Value == "" && prev.Value != "" {
+		out.Value = prev.Value
+	}
 	if out.Text == "" && prev.Text != "" {
 		out.Text = prev.Text
 	}