Phase 1: FAQ JSON endpoint

[neuromechanist]

Part of epic #321

Scope

Expose community-generated FAQ entries as a public, read-only JSON feed, gated per-community.

Tasks

• Privacy/quality spot-check of existing faq_entries on dev (author PII in answers, quality outliers)
• Add top-level public_feeds config block (faq: bool, citations: bool) to community config schema
• GET /{community_id}/faq read-only endpoint over search_faq_entries, gated by public_feeds.faq
• Filters: q, category, min_quality
• Expose only safe fields: question, answer, tags, category, quality_score, thread_url, message_count, first_message_date (no raw author PII)
• Tests against real dev data

Returns 404/disabled when public_feeds.faq is unset or false.