Feature: Nested Tags (#10833)

---------

Co-authored-by: Trenton H <797416+stumpylog@users.noreply.github.com>

src-ui/src/app/data/tag.ts

@@ -6,4 +6,12 @@ export interface Tag extends MatchingModel {
   text_color?: string
 
   is_inbox_tag?: boolean
+
+  parent?: number // Tag ID
+
+  children?: Tag[] // read-only
+
+  // UI-only: computed depth and order for hierarchical dropdowns
+  depth?: number
+  orderIndex?: number
 }