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/tui/commands.go

@@ -1,6 +1,11 @@
 package tui
 
 import (
+	"os"
+	"os/exec"
+	"time"
+
+	"github.com/atotto/clipboard"
 	tea "github.com/charmbracelet/bubbletea"
 
 	"github.com/lerko/nib/internal/db"
@@ -18,6 +23,29 @@ type entityDeletedMsg struct {
 	id string
 }
 
+type entityUpdatedMsg struct {
+	entity *db.Entity
+	action string
+}
+
+type entityPromotedMsg struct {
+	id string
+}
+
+type entityDemotedMsg struct {
+	id string
+}
+
+type entityCopiedMsg struct{}
+
+type tagsLoadedMsg struct {
+	tags []db.TagCount
+}
+
+type editorFinishedMsg struct {
+	err error
+}
+
 type errMsg struct {
 	err error
 }
@@ -49,3 +77,130 @@ func deleteEntity(store *db.Store, id string) tea.Cmd {
 		return entityDeletedMsg{id}
 	}
 }
+
+func toggleTodo(store *db.Store, e *db.Entity) tea.Cmd {
+	return func() tea.Msg {
+		var update db.EntityUpdate
+		if e.CompletedAt == nil {
+			now := time.Now().UTC()
+			update = db.EntityUpdate{CompletedAt: &now}
+		} else {
+			update = db.EntityUpdate{ClearCompleted: true}
+		}
+
+		if err := store.Update(e.ID, &update); err != nil {
+			return errMsg{err}
+		}
+		updated, err := store.Get(e.ID)
+		if err != nil {
+			return errMsg{err}
+		}
+		action := "completed"
+		if e.CompletedAt != nil {
+			action = "reopened"
+		}
+		return entityUpdatedMsg{updated, action}
+	}
+}
+
+func pinEntity(store *db.Store, e *db.Entity) tea.Cmd {
+	return func() tea.Msg {
+		newPinned := !e.Pinned
+		update := db.EntityUpdate{Pinned: &newPinned}
+		if err := store.Update(e.ID, &update); err != nil {
+			return errMsg{err}
+		}
+		updated, err := store.Get(e.ID)
+		if err != nil {
+			return errMsg{err}
+		}
+		action := "pinned"
+		if !newPinned {
+			action = "unpinned"
+		}
+		return entityUpdatedMsg{updated, action}
+	}
+}
+
+func promoteEntity(store *db.Store, id string) tea.Cmd {
+	return func() tea.Msg {
+		if err := store.Promote(id, db.CardSnippet, nil); err != nil {
+			return errMsg{err}
+		}
+		return entityPromotedMsg{id}
+	}
+}
+
+func demoteEntity(store *db.Store, id string) tea.Cmd {
+	return func() tea.Msg {
+		if err := store.Demote(id); err != nil {
+			return errMsg{err}
+		}
+		return entityDemotedMsg{id}
+	}
+}
+
+func copyToClipboard(store *db.Store, e *db.Entity) tea.Cmd {
+	return func() tea.Msg {
+		if err := clipboard.WriteAll(e.Body); err != nil {
+			return errMsg{err}
+		}
+		if err := store.IncrementUse(e.ID); err != nil {
+			return errMsg{err}
+		}
+		return entityCopiedMsg{}
+	}
+}
+
+func loadTags(store *db.Store) tea.Cmd {
+	return func() tea.Msg {
+		tags, err := store.ListTags(false)
+		if err != nil {
+			return errMsg{err}
+		}
+		return tagsLoadedMsg{tags}
+	}
+}
+
+func editInEditor(store *db.Store, e *db.Entity) tea.Cmd {
+	editor := os.Getenv("EDITOR")
+	if editor == "" {
+		editor = "vi"
+	}
+
+	f, err := os.CreateTemp("", "nib-edit-*.md")
+	if err != nil {
+		return func() tea.Msg { return errMsg{err} }
+	}
+	if _, err := f.WriteString(e.Body); err != nil {
+		f.Close()
+		os.Remove(f.Name())
+		return func() tea.Msg { return errMsg{err} }
+	}
+	f.Close()
+
+	c := exec.Command(editor, f.Name())
+	return tea.ExecProcess(c, func(err error) tea.Msg {
+		defer os.Remove(f.Name())
+		if err != nil {
+			return editorFinishedMsg{err}
+		}
+
+		content, readErr := os.ReadFile(f.Name())
+		if readErr != nil {
+			return editorFinishedMsg{readErr}
+		}
+
+		newBody := string(content)
+		if newBody == e.Body {
+			return editorFinishedMsg{nil}
+		}
+
+		update := db.EntityUpdate{Body: &newBody}
+		if updateErr := store.Update(e.ID, &update); updateErr != nil {
+			return editorFinishedMsg{updateErr}
+		}
+
+		return editorFinishedMsg{nil}
+	})
+}