feat: add XPS import and constrained fitting

[Limdongcheng]

Summary

Add XPS as a first-class PlotX data domain with validated VAMAS and CasaXPS import, dedicated processing state, constrained peak fitting, project persistence, export, and a complete desktop workbench.

• Import ISO 14976 VAMAS .vms experiments and structured CasaXPS .txt without intercepting ordinary text tables.
• Preserve measurement positions, spectrum regions, stable IDs, native/derived energy axes, acquisition metadata, and imported CasaXPS fits.
• Add position-level charge correction, XPS crop/smooth/normalize recipes, Linear/Shirley/Tougaard U2 backgrounds, constrained GL fitting, covariance diagnostics, and wild residual bootstrap.
• Persist XPS data, recipes, workspaces, imported and PlotX fits, provenance, and active selection in the current pre-release project format without changing schema/version constants or adding compatibility paths.
• Integrate XPS through existing field capabilities, actions, undo/redo, background jobs, command gating, export, screenshot harness, CLI inspection, recent files, and English/Chinese documentation.
• Keep Survey atomic percentages, sensitivity factors, automated chemical assignment, and the peak-assignment database out of scope.

Validation

• cargo pr-check
• npm run build - 73 documentation pages built
• Real-data UI regression with WBG250331.vms: 5 positions, 20 regions, reversed binding-energy axis, position 2 C 1s charge correction +4.80 eV, background preview, and explicit C 1s component template
• Screenshot harness: XPS Background, Components, narrow Components, and Diagnostics scenes
• git diff --check
• Confirmed project/data/settings/scheme schema/version constants remain 1
• Confirmed no reference instrument data or generated directories are included

UI display logic

• New or changed actions go through the command catalog (CommandId + describe) and are searchable in the command palette.
• Hiding happens only at Ribbon-group level (dataset kind or width budget); transient states disable with a disabled_reason that says how to unblock.
• No layout changes from background events; panels are never auto-closed.
• New panels or empty regions show an empty state with a next step.
• Docs updated in docs/ (English and zh-CN) for user-visible behavior.