PDF/.ai import: a .ai opens on its artboard with its bleed round it (#1266)

A PDF-compatible .ai with a bleed writes its PDF part's page as the
artboard grown by the bleed: the crop box takes the bleed in, the trim
box is the artboard and the bleed box the bleed. The importer made the
crop box the artboard, so the bleed opened as more white page with no
bleed guide; and since the editing data's artboard no longer matched
that page, its layers weren't read either ("its editing data is for a
different page").

Opening a PDF-compatible .ai with the crop box (the default) now takes
its trim boxes as the artboards. Any import on the trim boxes (Crop To
› Trim, for a PDF too) sets the document's bleed to how far the bleed
boxes reach past them on each side (ISO 32000-1, 14.11.2), kept to
0–72 pt, and the document read from the editing data keeps it. Art in
the bleed shows outside the artboard, within the bleed guide. Plain
PDFs still open on their crop box by default, and Place is unchanged.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/mcp.md

@@ -509,8 +509,9 @@ an EPS as its page, a `.ai` file from its PDF content (a `.ai` saved without PDF
 ```
 
 Opening a PDF (or `.ai`) imports every page as an artboard and layer; `document.open` takes `pages` ("2-3, 5", 1-based),
-`cropTo` (`bounding` (the art's bounds), `art`, `crop` (default), `trim`, `bleed`, `media`: the box each artboard gets)
-and `password` for an encrypted file. `document.pdfInfo` reads a file without opening it: the page count, each page's
+`cropTo` (`bounding` (the art's bounds), `art`, `crop` (default), `trim`, `bleed`, `media`: the box each artboard gets;
+with `trim` the bleed box round it becomes the document's bleed, and a PDF-compatible `.ai` opens on its trim boxes for
+`crop`, its crop box taking the bleed in) and `password` for an encrypted file. `document.pdfInfo` reads a file without opening it: the page count, each page's
 size and boxes, `needsPassword`, and with `thumbnail: n` a PNG of page n. Imported colours keep their model:
 DeviceCMYK and CMYK ICC colours stay CMYK (a file painted mostly in CMYK opens as a CMYK document), DeviceGray is Gray,
 and Separation and DeviceN inks become spot swatches the art links to at its tint (gradient stops too). CMYK images