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).

scripts/generate_test_files.py

@@ -1048,7 +1048,7 @@ def generate_pdf():
     p4.insert_text(
         (72, 430),
         "You can choose between several translation providers depending on your "
-        "needs: Google Translate (free tier), DeepL (premium), OpenAI GPT-4 "
+        "needs: Google Translate (free tier), OpenAI GPT-4 "
         "(premium, best for technical content), or Anthropic Claude (premium, "
         "best for literary content).",
         fontsize=11,