PDF/.ai import: spot inks with the same values and different names keep their own swatches

A PDF can define spot inks that have different names and the same
alternate space and tint transform, such as Blue1 and Blue2, both RGB
0 0 255. The interpreter drops the ink name, so the importer matches an
interpreted color to the file's Separation and DeviceN spaces by the
tint transform. The spaces of two such inks matched the same color, so
their paths imported as plain RGB and neither ink became a spot swatch.
This happened with both inks on one page, with each on its own page,
and in the PDF part of a .ai file.

The page walk in import_scan.rs, which follows the interpreter's order
for layers and overprint, now also records the ink of each path, from
the color space set by cs and CS or from the shading of the pattern set
by scn and SCN or drawn by sh, and the ink of the color space of the
text between two paths. When the spaces of several inks match a color,
the importer takes the space with the walk's ink names. It applies
these names to a page only when the page uses such an ink and a
counting pass of the interpreter draws as many paths there as the walk
counted. Otherwise the import works as before.

The file now opens with a spot swatch for each ink. Solid fills and
strokes of paths and type, and the stops of gradients on paths, link
to the swatch of their ink, the points of a gradient mesh keep the
ink's color, and PDF export writes each ink as its own separation.
Paint in these inks inside pattern cells, soft masks and type 3 glyphs,
and gradients on type in these inks, still import as RGB. Type in one
of these inks can also import as RGB when type in another Separation or
DeviceN ink is shown with no path drawn between them.

docs/target-app-parity.md

@@ -537,6 +537,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   The font database looks up a name that is neither a loaded nor an installed family among the other names of the loaded and installed fonts once for each style it is asked in, and keeps the answer until fonts are added or rescanned. Laying out a story of 1,000 paragraphs set in a font that is not installed, with 400 more fonts loaded, takes a median of 56 to 71 ms instead of 409 to 507 ms on Windows 11 (`CRAFT_FONTS_DIR=<craft-fonts checkout> cargo test --release -p vectorcraft-text --lib missing_font_story_layout_timing -- --ignored --nocapture`).
 - **Files (M4):**
   - PDF export and print composition use the optional shared guarded writer ([pdf-backend.md](pdf-backend.md)); app drawing and output policy and desktop printer submission remain in their existing layers. The shared reader keeps the app-owned import adapter; synthetic tests cover layer and overprint state across windows, long operands, inline images, failed decoding, document limits and incomplete tails. Empty and populated metadata key presence is regression-tested, and CI checks the immutable backend source.
+    A PDF, or a `.ai` read through its PDF part, whose spot inks have the same values but different names opens with a spot swatch for each ink. The solid fills and strokes of paths and type, and the stops of gradients on paths, link to the swatch of the ink they are painted in, the points of a gradient mesh in one of these inks keep the ink's color, and PDF export writes each of these inks as its own separation (`pdf/src/tests_import_color.rs`). Paint in these inks inside pattern cells, soft masks and type 3 glyphs, and gradients on type in these inks, still import as RGB. Type in one of these inks can also import as RGB when type in another Separation or DeviceN ink is shown with no path drawn between them.
   - `.vectorcraft` (lossless JSON, compressed, atomic saves, save down to v1), Save As with a format chooser, Save a Copy, Revert, templates, Data Recovery after a crash (browser tabs hold their copies with Web Locks too, so a background tab's copies are never taken for a crash's, and a tab repairs copies another removed when it resumes: #367), background save and export. The desktop app writes its warnings and errors (graphics adapter, a lost graphics device, panics the guard recovered from) to standard error and to `logs/vectorcraft.log` next to the preferences, the two previous runs kept and each file capped at 16 MiB, so a launch without a terminal still leaves something to attach to a bug report (#465). Native documents with a lot of path data (traced or generated art, in layers, symbols or patterns) are saved as compact JSON, about a fifth of the size; small documents stay pretty-printed (#1492). Saving to a network drive on macOS falls back to a plain fsync when the share refuses a full flush (#1625, part of #1620; not confirmed on a real share), and a save still succeeds when a folder refuses the temporary file, the rename over the document or copying permissions: the content is written elsewhere first and copied in, and a failed copy keeps the temporary file and names it (#1649, part of #1620). A document opened by a relative path finds its relatively linked images, and `vectorcraft-cli convert` lists what reading the input left out as `importWarnings` (#1606, fixes #1604).
   - SVG/SVGZ in and out with SVG Options, Preserve Editing, symbols, filters, rich text and physical units (SVG type under a transform or `viewBox` scale opens at the size it draws at, the scale moved into its size, leading, baseline shift and strokes, a stretch, skew or rotation kept as its transform: #396; a top-level group with a clip path, such as a clipped Inkscape layer, opens as a layer with a clipping mask, its name kept: #420; hidden objects written hidden on Save and `convert`, and `data-*` attributes kept as the objects' own data: #522; top-level groups open as layers named from `data-name`, else the id, also when one more group (a transform on all the art, a `<switch>`) wraps them, hidden ones hidden, and a file whose art sits loose under a root `<svg>` with an id (or `data-name`), as one-layer exports write it, opens with its one layer named from it; nested groups stay groups, except the sublayers VectorCraft writes, marked `data-vc-layer`, and Inkscape sublayers, which open as sublayers in their layer's colour: #372); PDF and PDF-compatible `.ai` in and out (layers, with hidden ones kept hidden with their art and nested ones as sublayers, on pages of up to 64 million operators, art whose layer can't be told going to a hidden, non-printing layer rather than showing or printing: #419; strokes kept live, a fill and a stroke of one outline as one object; a type object's stroke written as each glyph's outline stroked back on the type, so it stays one editable object; lines wrapped in a frame (each wrapped line ending in a space, one left edge, leading and font) back as one area type object, left aligned or justified with its paragraph spacing, where laying it out breaks the lines where the file does; glyphs set apart by gaps wider than a space (a barcode's digit groups) keeping their places; layers stacked as the pages mark them even when one first paints on a later page, art ending a layer's marked content or a clip closing in a later layer kept in its own layer, and layers with no art kept empty: #508; art reaching past a plain PDF's page clipped to its crop box, as PDF viewers show it, each such object in a clip group of its own (a PDF-compatible `.ai` opens whole: #675); a `.ai` on its trim boxes with the bleed boxes round them as the document's bleed, as Crop To › Trim opens a PDF (#1266); masks, editable text with type set along a curve coming back as type on a path, each artboard's art on its own page only, an `.ai`'s white page under its layers left out rather than coming in as art, spot colours, presets, security, marks and bleed, ICC output intents, raster effects, subset fonts, PDF/X, PDF layers, overprint, page thumbnails, fast web view, PDF 1.3). CMYK images keep their ink amounts from PDF import (and from placed CMYK TIFFs and the images in an `.ai` or EPS file's editing data, an alpha channel coming in as a grayscale opacity mask) to PDF export: a CMYK JPEG passes through unchanged, others stay CMYK (DeviceCMYK, or ICC-based CMYK in PDF/X-3/X-4) unless the Output settings convert them; the canvas shows them through the working CMYK profile (#320). Overprint is kept from PDF import (opened, the PDF part of an `.ai`, placed) to PDF export: the graphics state's `/OP` and `/op` become the overprint of fills, strokes and type, so a spot colour over a process colour still overprints; a page whose overprint can't be read for certain knocks out with a note, as does `/OPM 0` being read as nonzero overprint (#1388; hand-written fixtures, `pdf/src/tests_import_overprint.rs`). A masked CMYK image (`/SMask`, `/Mask` or a colour key) keeps its inks too, its alpha coming in as a greyscale opacity mask.
     SVG import's style cascade, used for hidden objects, non-scaling strokes and type, tests each element only against the `<style>` rules for its id, its classes and its element name, and the rules whose selector ends in none of these (`*`, `[x]`).