[mircealungu]

Switching language in the reader from a translated article made a new translation of the translation: Danish → Italian → Danish showed "Adapting..." again, called the LLM, and gave back the Italian adaptation in Danish instead of the original. Every further switch added another hop, because the #translated-from key kept growing and never hit the cache.

translate_and_adapt_article now follows the open article back to its original (reusing SharedArticle.resolve_original_article_id):

• Back in the original's language: returns the original, or its simplified version at the reader's level if there is one. No LLM call.
• Any other language: translates from the original, so the key is always <original>#translated-from-da-to-X-level and a language already visited comes from the cache.

Left as they were:

• Asking for an article's own language still adapts it, because the share flow's "Adapt" depends on that. The shortcut only applies when the open article is in another language.
• Translations of uploads keep translating from themselves, because the article at the upload's url may only be a paywall teaser. Further translations of them now carry source_upload_id, so this holds across hops.
• Translations made before this PR need no backfill, since the link is read from their url.

Also removes two local UserArticle imports in the function. They duplicated the module-level import and made the name unbound at the new early return.

Tests: 7 new cases in test_translate_and_adapt_article_switch.py; 6 of them fail without the fix (the seventh pins the unchanged same-language behavior). All 468 API tests pass. Not tried in a browser or on a device. API only, no migration.

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[github-actions]

ArchLens - No architecturally relevant changes to the existing views