feat(tui): add bubbletea terminal UI with entity list, detail, and capture

Adds `nib tui` command and `make tui` target. Scrollable entity list
with j/k navigation, enter for detail view, `a` to capture new entries
using the existing parse grammar, and `d` to delete.

internal/tui/commands.go

@@ -0,0 +1,51 @@
+package tui
+
+import (
+	tea "github.com/charmbracelet/bubbletea"
+
+	"github.com/lerko/nib/internal/db"
+)
+
+type entitiesLoadedMsg struct {
+	entities []*db.Entity
+}
+
+type entityCreatedMsg struct {
+	entity *db.Entity
+}
+
+type entityDeletedMsg struct {
+	id string
+}
+
+type errMsg struct {
+	err error
+}
+
+func loadEntities(store *db.Store, params db.ListParams) tea.Cmd {
+	return func() tea.Msg {
+		entities, err := store.List(params)
+		if err != nil {
+			return errMsg{err}
+		}
+		return entitiesLoadedMsg{entities}
+	}
+}
+
+func createEntity(store *db.Store, e *db.Entity) tea.Cmd {
+	return func() tea.Msg {
+		if err := store.Create(e); err != nil {
+			return errMsg{err}
+		}
+		return entityCreatedMsg{e}
+	}
+}
+
+func deleteEntity(store *db.Store, id string) tea.Cmd {
+	return func() tea.Msg {
+		if _, err := store.SoftDelete(id); err != nil {
+			return errMsg{err}
+		}
+		return entityDeletedMsg{id}
+	}
+}