feat(tui): add status bar, help overlay, tag filter, and entity actions

Status bar with entity count and context-sensitive key hints. Help
overlay via ? key. Tag filter via # with cursor-navigable tag list.
Todo toggle (x), pin (!), promote (p), demote (D), copy (c), edit (e)
via $EDITOR. Delete confirmation with 3s timeout. Date-grouped list
with completed todo and pinned indicators. Esc clears active tag filter.

Adds CompletedAt/ClearCompleted to EntityUpdate for todo toggling.

internal/db/entities.go

@@ -89,16 +89,18 @@ func DefaultListParams() ListParams {
 }
 
 type EntityUpdate struct {
-	Body        *string
-	Title       *string
-	Description *string
-	Glyph       *Glyph
-	TimeAnchor  *string
-	ClearTime   bool
-	Pinned      *bool
-	CardType    *CardType
-	CardData    *string
-	Tags        *[]string
+	Body           *string
+	Title          *string
+	Description    *string
+	Glyph          *Glyph
+	TimeAnchor     *string
+	ClearTime      bool
+	CompletedAt    *time.Time
+	ClearCompleted bool
+	Pinned         *bool
+	CardType       *CardType
+	CardData       *string
+	Tags           *[]string
 }
 
 func (s *Store) Create(e *Entity) error {
@@ -311,6 +313,12 @@ func (s *Store) Update(id string, u *EntityUpdate) error {
 		sets = append(sets, "time_anchor = ?")
 		args = append(args, *u.TimeAnchor)
 	}
+	if u.ClearCompleted {
+		sets = append(sets, "completed_at = NULL")
+	} else if u.CompletedAt != nil {
+		sets = append(sets, "completed_at = ?")
+		args = append(args, u.CompletedAt.Format(time.RFC3339))
+	}
 	if u.Pinned != nil {
 		sets = append(sets, "pinned = ?")
 		args = append(args, boolToInt(*u.Pinned))