i18n: missing translations never fail; xtask ci prints one report (#3856)

* i18n tests: report missing translations instead of failing

The scans for untranslated menu strings, tl! literals, undo labels, menu labels and status
messages print what a complete language lacks. A missing translation shows the English
text until a translator adds the row, so it no longer fails the gate.

* i18n: one untranslated report in xtask ci; drop one-language wording tests

`i18n::tests::untranslated_report` lists, per language, the menu strings, tl! literals, undo
step names and templates, menu labels, render-site labels, status and error messages,
PostScript error meanings and default swatch names its catalog lacks; strings every language
lacks are listed once. It never fails on a gap, only on a scan that finds too few strings.
`cargo xtask ci` runs it in an `i18n-report` step, and `cargo xtask i18n-report` runs it alone.

The five scan tests, the render-site and swatch coverage tests and untranslated_messages.txt
fold into the report. Tests that pinned one language's wording are gone; where they also
checked code (lookups, plural rules, locale tags, menu and History step names, engine
parameter errors), that check stays and compares with the catalog lookup.

docs/target-app-parity.md

@@ -549,10 +549,10 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - Panels undock (#495): a dock tab, a panel icon or a popped-out panel's title dragged out of the dock floats that panel inside the window, and the strip right of the dock's tabs floats the whole tabbed group. A floating group moves by its title bar, a tab dragged out of it floats on its own, and dropped on another group's title bar or tabs it stacks with that group; dropped on a dock group's tabs, which light up under the pointer, its panels join that group, and on the group's upper or lower half they make a new group above or below it (`window.panel.dock {anchor, zone}`); dropped on the icon column they become icons there, the tabbed group's panels too (`window.panel.dock {icon: true}`); dropped anywhere else on the dock, which lights up, they go back where they live (the tabbed group or the icon column), as its × and the panel menus' Float Panel / Dock Panel do (`window.panel.float`, `window.panel.dock`). The Tools panel floats by its title bar and docks again on the window's left edge. Floating groups stack into sets: dropped on the upper or lower half of another group (a line shows where), a group joins it right above or below it, and the set's groups stack top to bottom, each showing one panel, moving together by the top group's title bar, whose × docks them all; a group dragged by its tab strip leaves the set (`window.panel.float {below, above}`). A double-click on a tab collapses a floating group to its tabs (`collapsed`), and a dock group too, a group below it moving up into the room; a second double-click, or a click on another of its tabs, expands it (`window.panel.collapse`, kept with the preferences and in saved workspaces). Sets dropped on the left edge of the icon column or of another dock column dock as dock columns (a multi-column dock, `window.panel.dock {column}`), whose groups stack, tab and tear out as a floating set's do, and whose top strip floats the column again. Floating panels, their sets and the Tools panel's position are kept with the preferences and in user workspaces, and clamped into a smaller window. Not done: panels in separate OS windows, reordering tabs by dragging, collapsing a set or dock column to icons, dock columns right of the default dock, resizing floating panels and the groups of a set.
   - The dock's double arrow collapses Properties, Layers and Libraries to icons at the top of the icon column, popping out like the other icon panels, and expands them again (`window.collapseDock`, kept with the preferences and in saved workspaces). The icon column's own arrow (expanding the icon panels into a full column) is not done.
   - Czech render-site labels: desktop/web file filters, diagnostics, suggested preset names and contributor tooltips/plurals now use catalog lookups; gradients have Czech adjective agreement and printer marks have a separate context (PDF/Print and Summary). Search, Home, toolbar/panel tooltips and Preferences already look up their labels. Every complete catalog has rows for these labels and for the Roman and Japanese printer mark styles. Evidence: `i18n::tests::czech_render_site_follow_up`, `i18n::tests::complete_catalogs_translate_render_site_labels`, `dialogs::tests_modal::printer_mark_labels_are_distinct_from_language_names`; see [localization-parity.md](localization-parity.md).
-  - The History panel, Edit › Undo and Edit › Redo translate the names of the steps that apply or redefine a character or paragraph style and of the step that redefines a graphic style: each such step keeps its template (`Apply {name}`, `Redefine {name}`, `Redefine Graphic Style “{name}”`) and the style's name, every complete catalog has a row for each template, and the panel and the menu show the style's name as the document holds it, except the Normal styles' names, which they show in the interface language (`steps_named_after_a_style_list_the_template_around_the_name`, `undo_and_redo_name_a_style_step_around_the_style_name`, `every_undo_label_is_translated`).
+  - The History panel, Edit › Undo and Edit › Redo translate the names of the steps that apply or redefine a character or paragraph style and of the step that redefines a graphic style: each such step keeps its template (`Apply {name}`, `Redefine {name}`, `Redefine Graphic Style “{name}”`) and the style's name, every complete catalog has a row for each template, and the panel and the menu show the style's name as the document holds it, except the Normal styles' names, which they show in the interface language (`steps_named_after_a_style_list_the_template_around_the_name`, `undo_and_redo_name_a_style_step_around_the_style_name`).
   - Localised UI: menus (in-window and native), panels, dialogs, toolbar and Preferences read from per-language catalogs (`crates/ui-egui/src/i18n`, see `docs/development.md`); Traditional Chinese (Taiwan), Simplified Chinese (mainland), Japanese, Korean, Vietnamese, German, Spanish, French, Italian, Polish, Brazilian Portuguese, Russian, Ukrainian and Georgian ship complete, and Czech covers every menu label (and more), with system-locale detection on macOS, Windows, Linux and the web (the browser's languages, or `?lang=`), a Language preference and, on macOS, a VectorCraft ▸ Language menu. Names are never translated (fonts and their styles, layers, artboards, saved presets, user libraries, custom workspaces, recent files, plug-ins).
   - Edit › Undo and Edit › Redo, in the in-window and native menus, name the step in the interface language as the History panel lists it (`panels::history::step_name`), so when the catalog has no plain row for a step named after an effect, such as Feather, the menu shows the translation of the effect's menu row without its ellipsis (`undo_and_redo_name_the_step_as_the_history_panel_does`).
-  - The History panel translates the undo step names the engine, the tools and the shell write as literals: each has a row in every complete catalog (`every_undo_label_is_translated`), and a step whose catalog row exists only with an ellipsis (such as an effect's menu name) shows that row without the ellipsis.
+  - The History panel translates the undo step names the engine, the tools and the shell write as literals: the untranslated report (`untranslated_report`) lists any a complete catalog lacks, and a step whose catalog row exists only with an ellipsis (such as an effect's menu name) shows that row without the ellipsis.
   - The History panel menu has Step Backward and Step Forward, which run Edit › Undo and Edit › Redo and are disabled when there is no step to undo or redo, and Set History Limit…, which opens Preferences at Performance, where History States is set. Not done: a new document from the selected state.
   - The History panel menu's Clear History (`edit.clearHistory`) removes every step to undo and to redo and leaves the document as it is; it is not an undo step itself, and it is disabled when there is no step to clear.
   - Native macOS menu bar, vector tool cursors, a ⌘K command palette, middle-button panning with any tool. Native menus explicitly end tracking on command selection, outside window presses and Escape; menu updates wait until tracking ends, and a dismissing press never starts a canvas gesture (M14.8).