feat(tui): add search via capture bar and absorb flow

Search uses existing parse grammar ?prefix — type `?query #tag` in
capture bar to filter entities client-side. Substring match on
body+title+description with AND tag filtering. Esc clears search.

Absorb via m key on fluid entities — opens source picker showing all
other entities, enter merges source into target. Uses existing
store.Absorb() backend.

internal/tui/commands.go

@@ -40,6 +40,15 @@ type entityDemotedMsg struct {
 
 type entityCopiedMsg struct{}
 
+type entityAbsorbedMsg struct {
+	targetID string
+}
+
+type absorbSourcesLoadedMsg struct {
+	targetID string
+	entities []*db.Entity
+}
+
 type tagsLoadedMsg struct {
 	tags []db.TagCount
 }
@@ -207,3 +216,22 @@ func editInEditor(store *db.Store, e *db.Entity) tea.Cmd {
 		return editorFinishedMsg{nil}
 	})
 }
+
+func loadAbsorbSources(store *db.Store, targetID string) tea.Cmd {
+	return func() tea.Msg {
+		entities, err := store.List(db.DefaultListParams())
+		if err != nil {
+			return errMsg{err}
+		}
+		return absorbSourcesLoadedMsg{targetID, entities}
+	}
+}
+
+func absorbEntity(store *db.Store, targetID, sourceID string) tea.Cmd {
+	return func() tea.Msg {
+		if err := store.Absorb(targetID, sourceID); err != nil {
+			return errMsg{err}
+		}
+		return entityAbsorbedMsg{targetID}
+	}
+}