feat(ui/templates): derived-template action and slimmer composition row

Right-click a template now offers "New Derived Template" — opens
TemplateCreate with the parent pre-selected via a new ?parentId query
parameter. Composition rows in the tree drop the trailing
"→ TargetName" muted text; the kind glyph plus the instance name carry
enough meaning, and the composed template is one click away from the
row's right-click menu.

docs/requirements/Component-TreeView.md

@@ -425,7 +425,7 @@ Three node kinds; concrete recipes following V1–V6.
 |---|---|---|---|---|---|
 | Folder | `bi-folder` | `bi-folder2-open` | folder name (semibold when has children, regular otherwise) | — | count of direct children (subtle pill), only if ≥ 1 |
 | Template | `bi-file-earmark-text` | same (templates with compositions still use the same glyph — chevron carries state) | `$Name` (semibold when has compositions, regular otherwise) | — | none |
-| Composition | `bi-arrow-return-right` | n/a (leaf, no expanded state) | composition instance name (regular weight) | `<span class="text-muted small ms-1">→ $TargetName</span>` | none |
+| Composition | `bi-arrow-return-right` | n/a (leaf, no expanded state) | composition instance name (regular weight) | — | none |
 
 **`NodeContent` fragment** for the templates page (replaces the current `RenderNodeLabel` in `Templates.razor`):
 
@@ -452,13 +452,8 @@ Three node kinds; concrete recipes following V1–V6.
         break;
 
     case TmplNodeKind.Composition:
-        var composedName = _templates.FirstOrDefault(t => t.Id == node.Composition!.ComposedTemplateId)?.Name
-                           ?? $"#{node.Composition!.ComposedTemplateId}";
         <span class="tv-glyph"><i class="bi bi-arrow-return-right"></i></span>
-        <span class="tv-label" title="@node.Label">
-            @node.Label
-            <span class="text-muted small ms-1">→ @composedName</span>
-        </span>
+        <span class="tv-label" title="@node.Label">@node.Label</span>
         break;
 }
 ```