M4.20: Document Setup with bleed, transparency grid, paper and type options

File > Document Setup is a tabbed dialog over one engine command,
document.setup (no params: a query; any keys: one undo step;
document.setUnits stays as the units alias).

- General: units, bleed (four sides with a link toggle), Edit Artboards,
  Show Images in Outline Mode (greyscale pixels under the frame),
  Highlight Substituted Fonts/Glyphs (pink boxes on screen only).
- Transparency: grid size and colour presets or custom colours, Simulate
  Colored Paper, the flattener preset (built-in or saved) and Discard
  White Overprint (Overprint Preview keeps white overprints visible).
- Type: language with its quotes, Use Typographer's Quotes for the Type
  tool and Smart Punctuation, superscript/subscript size and position and
  small caps size (Character panel position/smallCaps; changing the
  setup restyles the text in the same undo step), text export (SVG text
  as text or outlines by default).
- The canvas draws a red bleed outline and the grid in the document's
  colours and cell size as one textured quad, also in rotated views; a
  white Background Contents exports raster formats opaque.

Model: Document.setup (DocSetup, defaulted, skipped when default) and
CharStyle position/small_caps; old files load unchanged.
tests_transparencygrid's helper now finds the grid by its texture (the
grid is one textured mesh instead of per-cell rectangles).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/control-protocol.md

@@ -204,3 +204,11 @@ length preferences in `preferences`) show in the General unit (the active docume
 document). Through `ui.dialog.set` a number is in points and a string may carry its unit (`"10 mm"`; a bare number in a
 string is points). The `preferences` dialog's `unitsGeneral` starts as the active document's units, and OK sets them.
 `newDocument` has `units` (a unit label; print presets start in `unitsGeneral`, screen presets in Pixels).
+
+Document Setup: File → Document Setup… (`file.documentSetup`, Cmd+Alt+P) opens the `documentSetup` dialog. Its fields
+are what `document.setup` reports (`units`, `bleed` [top, bottom, left, right] in pt, `outlineImages`,
+`highlightSubstitutedFonts`, `highlightSubstitutedGlyphs`, `gridSize`, `gridColors`, `simulatePaper`, `flattenerPreset`,
+`discardWhiteOverprint`, `language`, `quotes`, `typographersQuotes`, `superscript`, `subscript`, `smallCapsSize`,
+`exportText`, `backgroundContents`) plus `tab` (`General`, `Transparency` or `Type`) and `bleedLinked`.
+`ui.dialog.confirm` runs `document.setup` with them as one undo step; a bad value answers with an error and the dialog
+stays open.