feat(app): add trace stack composer

[nmrtist]

Summary

• Add a Trace Composer for building plots from selected items across compatible trace collections.
• Resolve trace applicability through field capabilities, concrete line encodings, and compatible unit contracts.
• Support electrophysiology sweeps and pseudo-2D increments through the same domain-neutral workflow.
• Preserve the existing immediate workflow for non-trace stacks.

User experience

• Open the composer from Stack selected data when compatible trace collections are selected.
• Start with every trace selected while allowing arbitrary subsets.
• Search by dataset source, semantic trace label, or parameter value.
• Provide Select all, Clear all, Select filtered, and Clear filtered controls.
• Show source filenames or custom dataset names, with deterministic disambiguation for duplicate names.
• Disable stack creation when no traces are selected.
• Keep cancellation and window dismissal free of document changes.
• Select and reveal the created plot automatically, fit its page to the workspace, and open its Data inspector section for immediate editing.
• Keep the composer responsive for narrow windows and large collections, with bounded rows, full-value tooltips, and accessible trace controls.

Data and lifecycle

• Keep composer drafts in transient session state.
• Address sources with stable dataset, field, and trace item identities.
• Revalidate every selected source before creating the plot.
• Preserve deterministic source ordering, palette colors, unique series IDs, and plot-owned bindings.
• Create the canvas as one undoable action.
• Preserve the selected traces through undo/redo and project save/load.
• Use the currently selected electrophysiology channel.
• Resolve pseudo-2D increments from the stable stack field even while DOSY or ILT maps are displayed.
• Keep the project schema fixed at version 1 without compatibility or migration logic.

Documentation

• Update the English and Simplified Chinese electrophysiology and pseudo-2D guides with the Trace Composer workflow.

Validation

• cargo pr-check
• Documentation build