6.16.2 Schema — add `publicTagline` + `publicTags` columns to Project + migration

Estimate: 40m · Type: code

Add two nullable/defaulted public-SAFE columns to the Project model, mirroring publicOverviewMd's shape (ride the public projection only when the project is public):

• publicTagline String? @map("public_tagline") — the hero subtitle; unset → generic i18n fallback.
• publicTags String[] @default([]) @map("public_tags") — the hero meta pills (Postgres text array).

Add a prisma migrate dev migration (pure column adds, no raw-SQL FK drift; existing projects backfill to NULL / []). Define PUBLIC_TAGLINE_MAX_LENGTH, PUBLIC_TAGS_MAX_COUNT, PUBLIC_TAG_MAX_LENGTH alongside PUBLIC_OVERVIEW_MAX_LENGTH.

Acceptance criteria

• Both columns in schema.prisma with doc comments mirroring publicOverviewMd.
• Migration committed; prisma migrate dev reports no drift after.
• Length/count constants defined.

Context refs

• prisma/schema.prisma Project (~381-387)