feat(pricing): remove DeepL from all user-facing surfaces

Pricing: 'deepl' removed from plan provider lists and the comparison
table row. Landing and pricing copy (13 locales) no longer mention
DeepL (65 values cleaned, 39 dead keys deleted: pricing.comparison.deepl,
providerTheme.classic.deepl.*).

Providers: available-provider responses are filtered so a DeepL entry
from the backend can never surface in the engine picker or the services
page; DeepL theme entry and static lib/api.ts list entry removed.

Admin: DeepL config card, type fields, defaults and fallback-chain
mentions removed; stats/chart/status maps and mock data cleaned.

Backend adapter untouched — DeepL is invisible app-wide via the UI
filter; removing the Python adapter itself is a separate step if wanted.

Verified: build exit 0, vitest 9/9, eslint clean on touched files,
zero 'deepl' occurrences outside the two intentional UI filters.

frontend/src/components/file-uploader.tsx

@@ -47,7 +47,7 @@ const fileIcons: Record<string, React.ElementType> = {
   ppt: Presentation,
 };
 
-type ProviderType = "google" | "ollama" | "deepl" | "libre" | "webllm" | "openai" | "openrouter";
+type ProviderType = "google" | "ollama" | "libre" | "webllm" | "openai" | "openrouter";
 
 interface FilePreviewProps {
   file: File;