feat(export): support images across export backends

[nmrtist]

Summary

• support embedded images across screen rendering, SVG, PDF, EMF, PNG, JPEG, TIFF, and figure clipboard output
• preserve source sampling, crop, rotation, opacity, interpolation, Panel clipping, and z-order during export
• add effective image PPI, resource availability, ICC profile, and high-precision color preflight checks
• keep projects editable when embedded images are missing or damaged, with diagnostics, replaceable placeholders, guarded saves, and explicit placeholder exports
• share decoded image data across repeated references and use bounded source-derived samples for oversized assets
• remove temporary image-export restrictions and redundant rendering adapters
• preserve full projected coordinate precision for dense spectral traces, preventing jagged curves when figures are pasted into Word
• add image export, degraded-resource, memory-sharing, EMF raster, and dense-spectrum regression coverage
• align the English and Simplified Chinese export, layout, file-format, and troubleshooting documentation

Testing

• cargo pr-check
• npm run build in docs/