fix(i18n): wrap hard-coded English strings in t() across UI (#6566)

## Summary
Audit + bulk fix of hard-coded English UI strings - `aria-label`,
`title`, `placeholder`, `label`, and raw JSX literals that bypassed i18n
entirely. Each literal now goes through `t("key", "English Default")`
from `react-i18next`, and every new key has a corresponding entry in
`en-GB/translation.toml` so translators can pick it up.

## What this fixes
Strings were rendered untranslated in every non-EN locale because they
never went through `t()` at all (not just "value not translated yet").
Affects screen-reader labels, tooltips, form placeholders, empty/loading
states, plan card content, and the entire workflow ParticipantView.

## Coverage (~143 keys / 50 files)
- **Viewer chrome** - search bar (close, clear, prev/next, "of N"
results), link/signature/redaction actions, viewer error state, zoom
labels
- **Page editor** - undo/redo/rotate/delete toolbar tooltips, empty
state, bulk selection operator chip tooltips
- **Shared primitives** - Tooltip close, InfoBanner dismiss, TextInput
clear, Toast dismiss/toggle, UpdateModal close, EditableSecretField
edit, DropdownListWithFooter search, FileCard/FileDropdownMenu actions,
EmptyFilesState + AddFileCard upload
- **Tools** - Image upload + hint, ColorControl eyedropper, sign Use
Signature, CompressSettings, OCR loading, PageLayout
margin/border/row/col placeholders, FormFill switch + save + re-scan
- **Proprietary admin** - OverviewHeader signed-in line + logout,
AdminPremiumSection moved-features list (via `<Trans>`),
AdminPlanSection no-data alert, AdminAdvancedSection temp-dir
placeholders, AdminEndpointsSection multiselect placeholders,
AdminMailSection + AdminDatabaseSection password placeholders
- **Onboarding** - MFASetupSlide QR loading + auth code label,
SecurityCheckSlide role select + options
- **ParticipantView** - entire sign-document UI (~30 strings: loading,
error, badges, headings, cert-type Select, all input labels and
placeholders, action buttons, completion + expired alerts) - file
previously imported `useTranslation` but only used `t()` for cert
validation
- **planConstants.ts refactor** - replaced `PLAN_FEATURES` /
`PLAN_HIGHLIGHTS` const exports with `usePlanFeatures()` /
`usePlanHighlights()` hooks. Service layer (`licenseService.getPlans`)
updated to accept feature/highlight maps so it stays hook-free. Callers
(`usePlans`, `CheckoutContext`) resolve the hooks at the React boundary
- **Previously catalogued offenders** - `FileSidebarFileItem`
open/close-viewer aria-labels, `quickAccessBar/ActiveToolButton` "Back
to all tools" tooltip + aria, `AppConfigModal` close button

## Notes
- One small refactor in `usePageSelectionTips.ts` was needed to resolve
a TOML key-shape conflict: the existing scalar keys
`bulkSelection.operators.{and,not,comma}` needed to become tables to
hold the new `.title` subkeys for OperatorsSection's chip tooltips. The
existing descriptions moved to `[bulkSelection.operators.descriptions]`
and the three i18n key paths in usePageSelectionTips were updated to
match.
- Viewer sidebar close buttons
(Bookmark/Layer/Thumbnail/Attachment/Comments) were on the audit list
but are NOT on main - they're added by the unmerged PR #6552
(feat/viewer-sidebar-ux). Those particular strings will need wrapping
when that PR lands.
- TOML hook (`toml-sort-fix`) ran and re-sorted the translation file.

## Test plan
- [ ] `task frontend:typecheck` passes (core + proprietary + desktop
variants)
- [ ] `task frontend:lint` passes
- [ ] Switching language to Deutsch / Русский: previously-English
`aria-label`s + tooltips + placeholders + plan card bullets now render
translated (when the locale has values) or fall back to the English
default (when it doesn't)
- [ ] Plan page bullet points in EN render unchanged
- [ ] Sign-document flow (ParticipantView) renders unchanged in EN

frontend/editor/src/proprietary/services/licenseService.ts

@@ -1,7 +1,10 @@
 import apiClient from "@app/services/apiClient";
 import { supabase, isSupabaseConfigured } from "@app/services/supabaseClient";
 import { getCheckoutMode } from "@app/utils/protocolDetection";
-import { PLAN_FEATURES, PLAN_HIGHLIGHTS } from "@app/constants/planConstants";
+import type {
+  PlanFeaturesMap,
+  PlanHighlightsMap,
+} from "@app/constants/planConstants";
 import type { LicenseInfo, PlanFeature } from "@app/types/license";
 
 export interface PlanTier {
@@ -102,9 +105,18 @@ const SELF_HOSTED_LOOKUP_KEYS = [
 
 const licenseService = {
   /**
-   * Get available plans with pricing for the specified currency
+   * Get available plans with pricing for the specified currency.
+   *
+   * Feature and highlight labels are passed in by the caller (a React hook /
+   * context that resolves them via `usePlanFeatures` / `usePlanHighlights`),
+   * which keeps this service free of React/i18n dependencies while still
+   * returning fully localized plan content.
    */
-  async getPlans(currency: string = "usd"): Promise<PlansResponse> {
+  async getPlans(
+    planFeatures: PlanFeaturesMap,
+    planHighlights: PlanHighlightsMap,
+    currency: string = "usd",
+  ): Promise<PlansResponse> {
     try {
       // Check if Supabase is configured
       if (!isSupabaseConfigured || !supabase) {
@@ -179,8 +191,8 @@ const licenseService = {
           currency: currencySymbol,
           period: "/month",
           popular: false,
-          features: PLAN_FEATURES.SERVER,
-          highlights: PLAN_HIGHLIGHTS.SERVER_MONTHLY,
+          features: planFeatures.SERVER,
+          highlights: planHighlights.SERVER_MONTHLY,
         },
         {
           id: "selfhosted:server:yearly",
@@ -190,8 +202,8 @@ const licenseService = {
           currency: currencySymbol,
           period: "/year",
           popular: true,
-          features: PLAN_FEATURES.SERVER,
-          highlights: PLAN_HIGHLIGHTS.SERVER_YEARLY,
+          features: planFeatures.SERVER,
+          highlights: planHighlights.SERVER_YEARLY,
         },
         {
           id: "selfhosted:enterprise:monthly",
@@ -203,8 +215,8 @@ const licenseService = {
           period: "/month",
           popular: false,
           requiresSeats: true,
-          features: PLAN_FEATURES.ENTERPRISE,
-          highlights: PLAN_HIGHLIGHTS.ENTERPRISE_MONTHLY,
+          features: planFeatures.ENTERPRISE,
+          highlights: planHighlights.ENTERPRISE_MONTHLY,
         },
         {
           id: "selfhosted:enterprise:yearly",
@@ -216,8 +228,8 @@ const licenseService = {
           period: "/year",
           popular: false,
           requiresSeats: true,
-          features: PLAN_FEATURES.ENTERPRISE,
-          highlights: PLAN_HIGHLIGHTS.ENTERPRISE_YEARLY,
+          features: planFeatures.ENTERPRISE,
+          highlights: planHighlights.ENTERPRISE_YEARLY,
         },
       ];
 
@@ -240,8 +252,8 @@ const licenseService = {
         currency: currencySymbol,
         period: "",
         popular: false,
-        features: PLAN_FEATURES.FREE,
-        highlights: PLAN_HIGHLIGHTS.FREE,
+        features: planFeatures.FREE,
+        highlights: planHighlights.FREE,
       };
 
       const allPlans = [freePlan, ...validPlans];