One editor per workflow hierarchy: nested workflows in any file open in place

[endrix]

Phases 1 and 2 of docs/proposals/single-editor-hierarchy.md (#63).

A diagram whose nested workflows live in other files opened a new editor for every one you drilled into: a tab per level, each with its own chat, a Run button that ran the workflow on screen, and its own layout.

The profile flag clientBehavior.nestedNavigation: 'in-place' | 'new-editor' controls this. The default is 'new-editor', so other products are unchanged. With 'in-place', every nested workflow in any file is a view inside the editor of the root (the file opened).

Navigation (client)

• Drill-down and the breadcrumb send a RequestModelAction for the defining file to the same editor, with the trail from the root.
• The navigation stack is keyed by the editor's root (stackKey).
• "Used By" goes in place to an ancestor already in the trail, or to a workflow of the editor's own document. A caller in another file opens as a new root with no trail, as decided in the proposal.
• New node menu item Open in Its Own Editor (server + client handler) opens a nested workflow's file as a root of its own.

Refresh (host)

• The refresh context is keyed by the editor the request came from (getDocumentUriForClientId), not the file requested, and it remembers shownSourceUri.
• Saves, external changes and live preview refresh the view that is shown. For another file the view reloads from disk, because live-preview content is the root's text.
• The refresh during and after a run reloads the editor's current view (file, workflow, trail) instead of jumping back to the root.

Root anchoring

• __calDiagramContext gains rootSourceUri, rootWorkflowName and trail. rootOfStack returns the first crumb in place, otherwise the first crumb in the editor's own file.
• ▶ Run, ⟲ and "Rerun from Here" use the root. Inside a nested view, "Rerun from Here" reruns the root-level instance the view is in (rerunActorFor), since the trace only has root-level steps.
• The chat panel sends the view's trail with the selection and each message. The turn context names the nested view and the file defining it (viewContextText).

Not in this PR

• The GLSP-MCP root/view split.
• Phases 3 to 5: secondary documents saved after undo/redo, the root watching every file in its trail, per-instance layout, and the hierarchy export with the outline.

The container-parity baseline gains the one new handler, dialogram.openInOwnEditor.

Tests

• in-place drill-down vs. a new editor (mouse listener);
• refresh of the shown file with its trail, from disk, and as before for the editor's own document;
• the root of a hierarchy in both modes, the rerun target, and the rerun handler from a nested view;
• Open in Its Own Editor (handler and menu: offered only for another file's workflow instance);
• the chat view context.

All workspaces pass, with neutrality 5/5 and typecheck 5/5. wfpy-ide turns the flag on in a separate PR.

https://claude.ai/code/session_015VK7fH1c4aKbexnq2QcuKU