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/config.py

@@ -60,12 +60,6 @@ class ProvidersConfig:
         os.getenv("GOOGLE_CLOUD_RETRY_DELAY", "1.0")
     )
 
-    # DeepL
-    DEEPL_ENABLED: bool = os.getenv("DEEPL_ENABLED", "false").lower() == "true"
-    DEEPL_API_KEY: str = os.getenv("DEEPL_API_KEY", "")
-    DEEPL_TIMEOUT: int = int(os.getenv("DEEPL_TIMEOUT", "30"))
-    DEEPL_MAX_RETRIES: int = int(os.getenv("DEEPL_MAX_RETRIES", "3"))
-    DEEPL_RETRY_DELAY: float = float(os.getenv("DEEPL_RETRY_DELAY", "1.0"))
 
     # OpenAI
     OPENAI_ENABLED: bool = os.getenv("OPENAI_ENABLED", "false").lower() == "true"
@@ -110,7 +104,7 @@ class ProvidersConfig:
     #
     # IMPORTANT: the registry-based fallback (translate_with_fallback) only
     # ever sees providers that _auto_register_providers() registers, i.e.
-    # google, deepl, openai, deepseek and minimax. The OpenAI-compatible
+    # google, openai, deepseek and minimax. The OpenAI-compatible
     # shims (openrouter, openrouter_premium, zai) and google_cloud are wired
     # directly in routes/translate_routes.py and are intentionally NOT part of
     # the registry fallback chain — listing them here would make
@@ -120,16 +114,16 @@ class ProvidersConfig:
     FALLBACK_CHAIN: List[str] = [
         name.strip()
         for name in os.getenv(
-            "PROVIDER_FALLBACK_CHAIN", "google,deepl,openai,deepseek,minimax"
+            "PROVIDER_FALLBACK_CHAIN", "google,openai,deepseek,minimax"
         ).split(",")
         if name.strip()
     ]
 
     # Mode-specific fallback chains
-    # Classic mode: Google Translate -> DeepL
+    # Classic mode: Google Translate -> Google Cloud
     FALLBACK_CHAIN_CLASSIC: List[str] = [
         name.strip()
-        for name in os.getenv("FALLBACK_CHAIN_CLASSIC", "google,deepl").split(",")
+        for name in os.getenv("FALLBACK_CHAIN_CLASSIC", "google").split(",")
         if name.strip()
     ]
 
@@ -166,7 +160,7 @@ class ProvidersConfig:
         Get settings for a specific provider.
 
         Args:
-            provider_name: Name of the provider (e.g., "google", "deepl")
+            provider_name: Name of the provider (e.g., "google", "openai")
 
         Returns:
             ProviderSettings for the requested provider
@@ -181,12 +175,6 @@ class ProvidersConfig:
                 base_url=None,
                 model=None,
             ),
-            "deepl": ProviderSettings(
-                enabled=cls.DEEPL_ENABLED,
-                api_key=cls.DEEPL_API_KEY if cls.DEEPL_API_KEY else None,
-                base_url=None,
-                model=None,
-            ),
             "openai": ProviderSettings(
                 enabled=cls.OPENAI_ENABLED,
                 api_key=cls.OPENAI_API_KEY if cls.OPENAI_API_KEY else None,
@@ -231,7 +219,7 @@ class ProvidersConfig:
             return False
 
         # Providers requiring API keys
-        providers_requiring_key = {"deepl", "openai", "openrouter", "google_cloud", "deepseek", "minimax"}
+        providers_requiring_key = {"openai", "openrouter", "google_cloud", "deepseek", "minimax"}
 
         if provider_name.lower() in providers_requiring_key:
             return bool(settings.api_key)