feat(ui,api): wave 3 — editorial pricing, real cancel, server history, DeepL purge

Pricing: full editorial redesign — serif card headers with accent pills
replace the colored font-black blocks, tone sweep across toggle/metrics/
features/CTAs, PLAN_COLORS removed; one design system app-wide.

Translate: decorative titles one step down (CTA hierarchy restored);
glossary and image-translation blocks hidden entirely for free users
(progressive disclosure — three controls for free).

Reviews: XLIFF hint line explains the exchange format; backend errors
routed through a friendly mapper (session/not-found/rate-limit/server).

Landing: fabricated hero UI cards (fake 'Context Engine' overlay)
removed — the photo no longer promises screens that don't exist.

Nav: single DashboardNavLinks component shared by sidebar and mobile
drawer (was duplicated markup).

API: GET /api/v1/translations (user job history, paginated; completed
jobs retained 24h) and POST /api/v1/translations/{id}/cancel —
cooperative cancellation with worker checkpoints before dispatch and
before finalisation, reserved quota released immediately. Translate
monitor now offers a real 'Cancel translation' next to 'Back to start';
recent-jobs list reads server history first, localStorage fallback.

DeepL purge (backend): provider module, registry registration, config
attrs/defaults, dispatch branch, admin settings schema + test branch,
legacy availability block, validation rules, plan provider lists,
error-code mappings, MCP enums, translator prompt mention, related
tests updated/removed. Fallback resolver skips unknown providers, so
stale chains containing 'deepl' degrade gracefully.

Verified: backend 110 tests passed; frontend build exit 0, vitest 9/9,
0 missing i18n keys, eslint 63 errors (vs 64 at HEAD).

middleware/validation.py

@@ -625,7 +625,6 @@ class ProviderValidator:
     SUPPORTED_PROVIDERS = {
         "google",
         "google_cloud",
-        "deepl",
         "openai",
         "openrouter",
         "openrouter_premium",
@@ -657,14 +656,7 @@ class ProviderValidator:
             )
 
         # Provider-specific validation
-        if normalized == "deepl":
-            if not kwargs.get("deepl_api_key"):
-                raise ValidationError(
-                    "La cle API DeepL est requise pour utiliser le fournisseur DeepL",
-                    code="missing_deepl_key",
-                )
-
-        elif normalized == "openai":
+        if normalized == "openai":
             if not kwargs.get("openai_api_key"):
                 raise ValidationError(
                     "La cle API OpenAI est requise pour utiliser le fournisseur OpenAI",