feat(app): unify plot navigation and display controls

[nmrtist]

Summary

Plot navigation and display-sensitivity controls previously shared overlapping
wheel modifiers, making it difficult to predict whether a gesture would change
the viewport or the rendered data. Raising a contour threshold could also wrap
a weaker sign back to a near-zero fallback ladder, revealing negative noise
instead of suppressing weak contours.

This change:

• makes plain scrolling zoom the x axis of 1D plots and both axes of 2D plots
• keeps pinch zooming both axes and axis-strip scrolling limited to that axis
• adds ambient Alt + drag box zoom
• uses Alt + scroll for display sensitivity:
  • y intensity on 1D plots
  • lowest contour level on contour plots
  • colour range on heatmaps
• shows the active wheel target and reports ambiguous contour/heatmap overlays
  instead of silently choosing a layer
• adds catalog-backed heatmap range span and centre properties, including
  Object inspector, Ribbon, command-palette, reset, undo and viewport-preserving
  presentation updates
• coalesces wheel property edits and defers repeated contour rebuilds until the
  gesture finishes
• ensures Esc, commands, tool changes and canvas resets correctly finish
  pending wheel-property gestures
• treats a positive contour threshold at or above one sign's peak as intentional
  suppression, rather than replacing it with a fallback ladder near zero
• adds regression coverage for asymmetric positive/negative contour peaks
• updates the English and Simplified Chinese guides and shortcut reference

Validation

• cargo pr-check
• npm run build from docs/ — 69 pages built
• git diff --check

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; unavailable heatmap and contour
  controls provide an actionable reason.
• No layout changes are triggered by background events; panels are never
  auto-closed.
• The new heatmap section follows the existing property-section availability
  and empty-state behavior.
• User-visible behavior is documented in English and zh-CN.