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).

tests/test_translate_endpoint.py

@@ -125,7 +125,7 @@ def client(users_file: Path, monkeypatch):
             "extra_credits": 0,
             "max_pages_per_doc": 50,
             "max_file_size_mb": 10,
-            "allowed_providers": ["google", "deepl"],
+            "allowed_providers": ["google"],
         }
 
     monkeypatch.setattr(
@@ -483,7 +483,7 @@ class TestQuotaExceeded:
                 "extra_credits": 0,
                 "max_pages_per_doc": 50,
                 "max_file_size_mb": 10,
-                "allowed_providers": ["google", "deepl"],
+                "allowed_providers": ["google"],
             }
 
         monkeypatch.setattr(
@@ -535,7 +535,7 @@ class TestQuotaExceeded:
                 "extra_credits": 0,
                 "max_pages_per_doc": 50,
                 "max_file_size_mb": 10,
-                "allowed_providers": ["google", "deepl"],
+                "allowed_providers": ["google"],
             }
 
         monkeypatch.setattr(