Person 3: multilingual translation layer with tests and pipeline inte…

[ayushunhale10-code]

What changed

Implemented the multilingual translation layer (Person 3) for the voice FAQ feature:

• translateToEnglish(text) — translates any input text to English via AiClient, returns original if already English
• translateFromEnglish(text, targetLang) — translates English text into a target language
• detectLanguage(text) — identifies input language, falls back to English on failure
• processMultilingualQuery(text) — main pipeline entry point returning { translatedText, detectedLanguage, isEnglish }
• All functions have safe fallback to English on any AI/network failure
• Integrated into rag.service.ts (Ask AI/RAG pipeline) and search.controller.ts (standard FAQ search)

Related issue

Type of change

• Bug fix
• Feature
• Refactor (no behaviour change)
• Docs / comments only
• CI / tooling

Area affected

• Backend (Express / Mongoose)
• Frontend (React / Vite)
• Admin / Train tab (/admin/*)
• Community (/community — posts, comments, auto-answer)
• Search (hybrid text retrieval, training stats)
• Auth / middleware / samagama.in bridge
• Crons / schedulers / embedding-warm
• Observability (Sentry / logging / Discord alerts)
• Docs

CI verification

• cd apps/backend && npx tsc --noEmit exits 0
• cd apps/backend && npx vitest run — all tests pass
• cd apps/frontend && npx tsc --noEmit exits 0
• cd apps/frontend && npx vitest run — all tests pass
• pnpm run lint — 0 errors (152 warnings is the baseline)
• GitHub Actions green on the merge commit (CI, CodeQL, Build & Deploy)
• Tested with a real API hit or browser interaction if behaviour changed
• Tests added or updated for the change
• Single logical change — unrelated fixes noted in description, not fixed here
• Docs updated if route / API / env var / pipeline behaviour changed
• Rebased onto main, no merge commits

Notes for reviewer

Feature type 'translation' was added to AiClient's AIFeature union to support this. 11/11 unit tests passing in multilingual.service.test.ts (mocked AI responses — no live API calls in tests). Ready for integration with Person 5's pipeline.