One shared colour visitor (`colorcmds::Recolor`, used by Edit Colors, Recolor Artwork, the Blend
commands, the proxy Invert/Complement and Document Color Mode) maps solid colours, gradient stops
and text runs as before, and now also:
- gradient-mesh points (with fills); Blend grades meshes by their average and keeps their shading;
- embedded images' pixels (`includeImages?`, default on): the image becomes a recoloured copy under
a content key, the original stays for undo and other objects; linked images are left alone;
- the tiles of pattern fills and strokes (`includePatterns?`, default on): one recoloured copy per
pattern saved as a new pattern swatch ("Dots 2"), the original untouched.
Everything stays one undo step; only nodes that change are copied, in one walk of the tree.
- doc: `ImageBlob::map_rgb` (decode, map each distinct colour once, keep alpha, re-encode PNG),
`ImageBlob::content_key` (now also used by image import) and `ImageBlob::png`.
- `recolor.colors` lists mesh points and pattern tile colours too.
- patterncmds: `add_pattern` adds a pattern and its swatch (shared by Make Pattern and Save a Copy).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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