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/input.go

@@ -8,6 +8,13 @@ import (
 	"github.com/lerko/nib/internal/parse"
 )
 
+type inputResult struct {
+	entity *db.Entity
+	query  bool
+	body   string
+	tags   []string
+}
+
 type inputModel struct {
 	ti     textinput.Model
 	active bool
@@ -32,7 +39,7 @@ func (i *inputModel) reset() {
 	i.ti.Blur()
 }
 
-func (i inputModel) submit() *db.Entity {
+func (i inputModel) submit() *inputResult {
 	val := i.ti.Value()
 	if val == "" {
 		return nil
@@ -43,6 +50,14 @@ func (i inputModel) submit() *db.Entity {
 		return nil
 	}
 
+	if parsed.Query {
+		return &inputResult{
+			query: true,
+			body:  parsed.Body,
+			tags:  parsed.FilterTags,
+		}
+	}
+
 	e := &db.Entity{
 		Body:  parsed.Body,
 		Title: parsed.Title,
@@ -63,7 +78,7 @@ func (i inputModel) submit() *db.Entity {
 		e.Description = parsed.Description
 	}
 
-	return e
+	return &inputResult{entity: e}
 }
 
 func (i inputModel) updateKey(msg tea.KeyMsg) inputModel {