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).

services/providers/__init__.py

@@ -16,7 +16,7 @@ Usage:
     response = google_provider.translate_text(request)
 
     # Use fallback chain
-    provider = registry.get_first_available(["google", "deepl", "openai"])
+    provider = registry.get_first_available(["google", "openai"])
 """
 
 from .base import TranslationProvider
@@ -54,13 +54,6 @@ def _auto_register_providers() -> None:
     if ProvidersConfig.GOOGLE_ENABLED:
         register_google_provider()
 
-    if ProvidersConfig.DEEPL_ENABLED and ProvidersConfig.DEEPL_API_KEY:
-        from .deepl_provider import register_deepl_provider
-
-        register_deepl_provider()
-
-
-
     if ProvidersConfig.OPENAI_ENABLED and ProvidersConfig.OPENAI_API_KEY:
         from .openai_provider import register_openai_provider