Move composition CRUD off the TemplateEdit page and onto the tree
context menu, matching Aveva's Template Toolbox flow.
- New ComposeIntoDialog: pick a parent template, slot name (defaults
to the source template's name).
- "Compose into…" on every base template's context menu (kebab + right
click) opens the dialog and calls AddCompositionAsync.
- "Rename…" on composition leaves opens a prompt and calls
TemplateService.RenameCompositionAsync. The owning composition row
AND its owned derived template are renamed atomically; duplicate
slot names or derived-name collisions abort with a clear error.
- "Delete" on composition leaves confirms + cascade-deletes the
composition (and its derived template via DeleteCompositionAsync).
- "New Derived Template" menu item renamed to "New Inheriting Template"
to disambiguate from the new derive-on-compose meaning.
TemplateEdit's Compositions tab, Add Composition form, and
Add/DeleteComposition handlers + state fields are deleted — the tree
is now the single source of truth.
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