feat(tui): stumble mode — resurface stale entries card by card

Card-by-card walkthrough of entries untouched for 30+ days.
Prevents write-mostly decay by bringing old entries back to attention.

- S from list triggers stumble, loads entries where modified_at < 30d
- Single-card view with markdown body, glyph, tags, age indicator
- Actions: n skip, d dismiss, ! pin, p promote, m absorb, esc exit
- Progress indicator: stumble [3/12]
- After promote/absorb from stumble, returns to deck (not list)
- "All caught up" screen when deck exhausted
- DB: add ModifiedBefore to ListParams, modified_at sort column

internal/tui/commands.go

@@ -62,6 +62,14 @@ type railTagsLoadedMsg struct {
 	tags []db.TagCount
 }
 
+type staleEntitiesLoadedMsg struct {
+	entities []*db.Entity
+}
+
+type stumbleActionMsg struct {
+	action string
+}
+
 type statusClearMsg struct{ seq int }
 
 type editorFinishedMsg struct {
@@ -289,3 +297,33 @@ func clearStatusAfter(d time.Duration, seq int) tea.Cmd {
 		return statusClearMsg{seq: seq}
 	})
 }
+
+func loadStaleEntities(store *db.Store) tea.Cmd {
+	return func() tea.Msg {
+		entities, err := store.List(staleParams())
+		if err != nil {
+			return errMsg{err}
+		}
+		return staleEntitiesLoadedMsg{entities}
+	}
+}
+
+func stumbleDismiss(store *db.Store, id string) tea.Cmd {
+	return func() tea.Msg {
+		if _, err := store.SoftDelete(id); err != nil {
+			return errMsg{err}
+		}
+		return stumbleActionMsg{"dismissed"}
+	}
+}
+
+func stumblePin(store *db.Store, id string) tea.Cmd {
+	return func() tea.Msg {
+		pinned := true
+		update := db.EntityUpdate{Pinned: &pinned}
+		if err := store.Update(id, &update); err != nil {
+			return errMsg{err}
+		}
+		return stumbleActionMsg{"pinned"}
+	}
+}