docs(templates): describe folder hierarchy and management commands

docs/requirements/Component-TemplateEngine.md

@@ -23,6 +23,7 @@ Central cluster only. Sites receive flattened output and have no awareness of te
 - Perform comprehensive pre-deployment validation (see Validation section).
 - Provide on-demand validation for Design users during template authoring.
 - Enforce template deletion constraints — templates cannot be deleted if any instances or child templates reference them.
+- Organize templates into nested folders (`TemplateFolder` entity) and validate folder hierarchy invariants (acyclicity, sibling uniqueness, non-empty-on-delete).
 
 ## Key Entities
 
@@ -33,6 +34,14 @@ Central cluster only. Sites receive flattened output and have no awareness of te
 - Defines attributes, alarms, and scripts as first-class members.
 - Cannot be deleted if referenced by instances or child templates.
 - Concurrent editing uses **last-write-wins** — no pessimistic locking or conflict detection.
+- May belong to a `TemplateFolder` via nullable `FolderId`, or live at the tree root when null.
+
+### TemplateFolder
+- Hierarchical organizational entity with a self-referencing `ParentFolderId` (null at the root).
+- Sibling folder names are unique (case-insensitive) within the same parent.
+- Folders carry **no semantic meaning** for template resolution, flattening, validation, or inheritance — they exist purely for UI organization.
+- Folder deletion is blocked if the folder contains any subfolders or templates.
+- The folder graph is enforced acyclic on move (a folder cannot become its own descendant).
 
 ### Attribute
 - Name, Value, Data Type (Boolean, Integer, Float, String), Lock Flag, Description.