Add internship-phase based FAQ personalization

[vedhashree06]

What changed

Added internship phase-based FAQ filtering to improve the FAQ experience for students. FAQs can now be filtered according to the student's current internship phase, allowing students to see FAQs that are relevant to their current stage of the internship instead of viewing unrelated phase-specific FAQs. The changes update the backend FAQ and internship-related logic to support phase-based FAQ visibility while retaining general FAQs.

Related issue

Not applicable.

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
• Docs
• Crons / schedulers / embedding-warm
• Observability (Sentry / logging / Discord alerts)

CI verification

• Docs updated if route / API / env var / pipeline behaviour changed
• 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
• Rebased onto main, no merge commits
• 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

Notes for reviewer

The main purpose of this change is to make FAQ visibility more relevant to the student's internship progress. General FAQs remain available, while phase-specific FAQs can be shown based on the student's current internship phase. The implementation is focused on the backend FAQ/internship logic and does not introduce unrelated changes.