6.16.3 Backend — thread `publicTagline`/`publicTags`/`viewerCanManage` through read/write

Estimate: 55m · Type: code · Depends on: 6.16.2

Thread publicTagline + publicTags + viewerCanManage through read + write (4-layer).

Read: add publicTagline: string | null and publicTags: string[] to PublicProjectOverviewDto + mapper (public-safe, only when public); surface via publicProjectsService.getOverview / lib/publicProjects/viewerContext. Add viewerCanManage: boolean (from the actor session + projectAccessService canManage) so the page can gate the Edit affordance server-side.

Write: generalize the 6.12.8 write path to author all three fields — extend projectsService.setPublicOverview (accept optional publicTagline, publicTags alongside publicOverviewMd) + projectRepository.setPublicOverview + the updateProjectOverviewAction input. Validation: trim; empty tagline → null; cap tagline at PUBLIC_TAGLINE_MAX_LENGTH; tags: trim each, drop empties, dedupe, cap count at PUBLIC_TAGS_MAX_COUNT and each at PUBLIC_TAG_MAX_LENGTH; typed errors (ProjectTaglineTooLongError, ProjectTagsInvalidError). Admin-gated via assertCanManage; one transaction.

Acceptance criteria

• Public overview DTO carries publicTagline, publicTags, viewerCanManage; non-public / non-admin reads never leak edit ability.
• One server action persists all three; validated + admin-gated; returns a DTO (no raw Prisma); typed errors mapped.
• Service/unit tests for the gate + tagline length + tags count/length (per-file coverage gate).

Context refs

• lib/dto/publicProjects.ts, lib/mappers/publicProjectsMappers.ts, lib/services/publicProjectsService.ts, lib/publicProjects/viewerContext.ts
• lib/services/projectsService.ts setPublicOverview (~664-685), lib/repositories/projectRepository.ts (~293-298)
• app/(authed)/settings/project/actions.ts updateProjectOverviewAction (~84-112); projectAccessService.assertCanManage