Fix duplicate/delete node transforms and selection updates

[cbassuarez]

Motivation

• Duplicate/Delete editor actions were no-ops because command handlers did not emit canonical transform requests and keyboard shortcuts weren't wired to transforms.
• The server-side edit API lacked canonical handlers for deleteNode/duplicateNode, so UI requests couldn't reliably update the document or selection.
• Selection remained stale after node operations because transform responses didn't include updated selection logic.

Description

• Wired editor commands to real handlers by adding handleDuplicate/handleDelete into the command context and hooking Duplicate/Delete menu commands and shortcuts to emit transform requests.
• Split the editor transform entrypoints: introduced runTransform and exposed handleTransform (for TransformRequest) and handleEditorTransform (for internal EditorTransform) to avoid request-shape mismatches.
• Implemented server-side edit handlers for new ops: applyDeleteNodeTransform and applyDuplicateNodeTransform, plus helpers findNodeWithParent, cloneNodeWithNewIds, and applyReplaceBodyNodesTransform, to update the source, index, and returned selectedId appropriately.
• Updated the editor UI to call the canonical transform shape ({ op: ..., args: { id } }) for duplicate/delete and to update selection behavior: after delete select next sibling/prev/parent, after duplicate select the new copy.
• Added integration tests covering duplicate/delete behavior at the edit API level to guard tree+index updates and selection changes.

Testing

• Ran pnpm vitest packages/viewer/tests/edit-api.spec.ts; all tests passed (9 tests, 1 file), including the new duplicate/delete tests.
• The changes were exercised by the added tests that assert document source, index presence, and returned selectedId after operations.

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Codex Task