feat(ui): Step and Repeat dialog with Create as a grid and Preview

Edit > Step and Repeat opened the generic command form (Count 1..1000, Dx, Dy, Rows, Columns, Ids). It now has InDesign's dialog: Repeat (Count, or Rows and Columns when Create as a grid is on), Offset (Vertical, Horizontal, in the document's ruler units or any unit typed) and Preview, which shows the copies on the page while the dialog is open. Cancel, Esc and ui.dialog.cancel take the preview away; OK makes the copies once, as one undo step. A value that isn't a number keeps the dialog open and says so.

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

docs/target-app-parity.md

@@ -276,7 +276,7 @@ It is evidence of breadth: each item exists. It is not a claim of InDesign-level
 - Tables (M8): tables anchored in stories (header/footer/body rows, merged cells, per-edge strokes, fills + alternating fills, insets, vertical justification, at-least/exact row heights); composed into the text column (columns scale to fit, rows break across columns/frames with repeating headers/footers, overset); rendered, exported to PDF (real text) and IDML (export + import); Table menu, Table panel, Create Table dialog, caret/typing/Tab navigation and cell selection in cells; `table.*` commands.
 - Hyperlinks (text or frames → URL / e-mail / page) and bookmarks, exported as PDF link annotations and outline.
 - EPUB 3 (reflowable) export: stories in reading order, CSS from paragraph/character styles, images, navigation (`file.exportEpub`, CLI `--export x.epub`).
-- Data Merge (one linked CSV, TSV, text, or Excel file; text, image, QR, and hyperlink placeholders; preview; a new document with one record per page or records tiled on a single page), spell checking (public-domain Moby list + document dictionary, suggestions), Step and Repeat (count or grid), snippets, object styles, Numbering & Section Options.
+- Data Merge (one linked CSV, TSV, text, or Excel file; text, image, QR, and hyperlink placeholders; preview; a new document with one record per page or records tiled on a single page), spell checking (public-domain Moby list + document dictionary, suggestions), Step and Repeat (count or grid, with a previewing dialog), snippets, object styles, Numbering & Section Options.
 - Footnotes: Type › Insert Footnote (caret moves into the note), Document Footnote Options (numbering style incl. symbols, start/restart per page/spread/section, prefix/suffix, reference position/character style, paragraph style, separator, spacing, first baseline, rule above); notes composed at the bottom of the referencing column with the body text making room; edited in place on the canvas; rendered, exported to PDF (real text) and IDML (InDesign's structure, verified opening in InDesign 2026) and imported from IDML; `footnote.*` commands.
 - Paragraph Rules: Rule Above / Rule Below (on, weight, colour, tint, column or text width, offset, left/right indent) set in Type › Paragraph Rules…, the Paragraph panel menu and Paragraph Style Options › Paragraph Rules; inherited style values shown, and `type.para` / `style.paragraph.edit` change only the rule fields named.
 - Cross-references and text anchors: Insert Cross-Reference (paragraph by style, or text anchor), 11 formats with InDesign's building blocks (full/partial paragraph, paragraph text/number, page number, anchor name, chapter, file name) plus user formats; resolved live at composition — never out of date, no Update step; unresolved destinations show `??`; PDF link annotations to the destination page; IDML export/import as InDesign cross-reference sources, hyperlinks, text destinations and formats (verified in InDesign 2026); `xref.*` / `anchor.*` commands.