Image Trace: Document Library fills link to the document's global swatches

Squashed from #4396 onto main.

docs/image-trace-adjustments.md

@@ -46,6 +46,11 @@ most `colors` of its colors are used. A missing group and a group with no solid
 mode, palette or library in the panel clears the group. A group the active document does not have shows as All
 and traces as All.
 
+**Document Library linked colors.** With Library › Document Swatches, with or without a color group,
+a traced fill or stroke whose color comes from a global or spot swatch is linked to that swatch, and
+one whose color comes from a tint swatch is linked to its base at the tint. Editing the swatch
+recolors the trace. Colors from process swatches and from swatch libraries are not linked.
+
 **Document Library** traces with the library's colors as they are. Each pixel takes the library
 color nearest to it in lightness and hue, with a difference in hue or chroma counted three times
 as much as one in lightness, so a gray or a muted brown takes a black, white or other neutral

docs/target-app-parity.md

@@ -835,6 +835,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   Disable, Enable, Unlink and Link Opacity Mask and Opacity Mask Options (`transparency.setOpacityMask`) record no undo step when every mask they act on already has the flags they set.
 - **Image Trace, thin closed outlines:** generated `fit::snap_area_tests` verify nonzero interiors after straightening, opposite closed-boundary winding and Noise controls; see [quality notes](image-trace-quality.md#thin-closed-outlines-with-snap-curves-to-lines). Scores and hours unchanged; open-piece fitting is unchanged.
 - **Image Trace, Document Library color groups:** with Document Swatches, the panel's Colors menu and `"colorGroup"` trace with one color group's colors instead of every swatch, as the public panel documentation describes Document Library; code-drawn tests in `crates/engine` and the panel.
+- **Image Trace, Document Library linked colors:** with Document Swatches, traced fills and strokes from global and spot swatches (and tints of them) are linked to their swatches, so editing a swatch recolors the trace; process colors and swatch-library colors stay unlinked; a code-drawn test in `crates/engine`.
 - **Image Trace, flattened slivers:** in a Color, Grayscale or Black and White trace with Fills, a traced region whose outline straightens onto one line (a single pixel, or a one-pixel row along an edge, its pieces shared with the regions beside it) is left out instead of becoming a selectable path with no area, which paints nothing. Snap Curves To Lines straightens more outlines, so it leaves out more of these. Without Fills, the region's 1 px stroke draws it, and it is kept. Code-drawn tests in `crates/trace`.
 - **Image Trace, Auto Color rare colours:** the Automatic palette keeps colours too rare for its area count when they are distinct (Oklab) and drawn as coherent regions, at most six, protected from mixed-colour merging and Noise; code-drawn stem, highlight, low-contrast and scattered-noise tests (see [quality notes](image-trace-quality.md#auto-color-keeps-rare-colours)).
 - **Image Trace, Document Library keeps neutral tones neutral:** each pixel takes the library color nearest in Oklab with differences in hue and chroma counted three times, so a gray or a muted brown traces as a neutral library color instead of a saturated one of similar lightness; a code-drawn test of gray and brown patches with a black, light and blue library in `crates/trace`.