Swatches: the delete prompt for several swatches uses each language's plural forms

The confirmation for deleting several swatches and groups now goes
through i18n::tn, as the Graphic Styles prompt does, and each catalog
gives the count-dependent forms in an @plural row.

docs/target-app-parity.md

@@ -912,6 +912,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - **CSS swatch libraries:** fractional linear and radial gradient stop positions are preserved, so nearby stops such as 12.5% and 12.890625% remain distinct instead of collapsing to 13%. Reference: [CSS Images 3 color stops](https://www.w3.org/TR/css-images-3/#color-stop-syntax). The original synthetic regression is `palette_io::tests::css_preserves_fractional_gradient_stop_positions` in `crates/color/src/palette_io.rs`. Scores and hours are unchanged.
   - **Swatches:** names follow the colour model and are unique; Swatch Options (process/spot, Global, Gray/RGB/HSB/CMYK/Web, live preview); editing a global or spot swatch recolours every linked fill, stroke and text run in one undo step; multi-select and delete with confirmation; New Swatch and New Color Group dialogs (a group from the selected artwork's colours); swatches in colour groups convert, separate and count like any other. The Swatches panel selects ranges and whole groups, has a find field, and drags swatches to reorder, regroup or paint art; Add Used Colors, Select All Unused, Merge, Ungroup and Sort by Kind; a CMYK document keeps applied colours in CMYK. Swatch libraries: nine generated colour libraries and five gradient libraries in a library panel, saved as `.vcswatches`, `.gpl`, swatch exchange (`.ase`) or CSS, and loaded from `.vcswatches`, `.gpl` and `.ase` files (`.ase` both ways: RGB, CMYK, Lab and Gray; global, spot and process; groups) and from color books (`.acb`, read only: the RGB, CMYK or Lab colors of a book such as a Pantone book a user owns, named with its prefix and suffix, spot unless it says process, #831); `swatch.library.copyToUser` copies a loaded library into the User Defined folder without replacing a file, and a file with the same extension and bytes as a User Defined library opens as that library. Tints of global and spot colours ("Name 40%") stay linked and separate as a percentage of their plate. Spot colours can be defined in Lab (Spot Colors options). A built-in [Registration] swatch prints on every plate.
     Editing, renaming, deleting or merging a global swatch also changes the colors linked to it in graph designs, the art of brushes and the tile that pattern editing's Cancel puts back, in the same undo step as the rest of the art; Default Swatches with replace unlinks them there too.
+    The prompt for deleting several swatches and groups uses the interface language's plural form for the count. Evidence: `deleting_several_swatches_uses_each_count_form` in `crates/ui-egui/src/panels/swatches/tests.rs`.
   - **Colorized images (#1466):** a fill color applied to a selected grayscale or 1-bit image (`paint.setFill`) colorizes it with black, white, a process color or a spot color, and refuses a process color when the image has an alpha channel ([Convert color modes](https://web.archive.org/web/20251220223850/https://helpx.adobe.com/illustrator/desktop/manage-colors/select-and-adjust-colors/convert-color-modes.html), "Colorize Grayscale or 1-bit images"); black and white are accepted there too. The canvas draws each pixel in the color as far as the pixel is dark, with white pixels transparent; PDF export writes the image in the color (a spot color as its ink, Registration in every ink) with the image as its soft mask; Separations Preview and printed separations show it on its color's plates; native files keep the color. EPS and SVG write the image's own pixels.
   - **Missing library files:** a persistent swatch or graphic style library panel whose file is gone at startup reopens and stays in the preferences, showing the file's path with Locate Library… (`ui.libraryPanel.locate`), which reads the file from where it is now into the same panel.
   - **Swatch library and Recolor Artwork parameters:** the `swatch.library.*` commands, `swatch.resetDefaults`, the graphic style library save, load and add, the `recolor.*` commands and `color.harmony`'s `limitTo` refuse parameters of the wrong form, such as `names: "Grays"`, `limitTo: 5` or `includeImages: "false"`. Errors name the parameter, except that a `limitTo` that is not a string, such as `5`, gets an unknown-library error. A `null` counts as left out except for `recolor.apply`'s `model`, which must be a string when given.